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Disappointed in towing performance

GearHead71
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Ray Pickle Enthusiast

Ray Pickle

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I can only guess there is a powertrain issue in your truck. This truck would benefit from a deeper axle ratio, but in my personal experience I have not had ANY problems maintaining 55 up any pass I have been on. That includes numerous passes through the continental divide. I will admit that I will typically pull a grade like the Eisenhower tunnel pass at 40 to 45 mph just because it is easier on the truck and therefore my wallet. That being said those grades are the rare exception both in grade and elevation. 

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Londart2020
Londart2020

And probably only weighed 4500 lbs, and the new truck is more than likely 7500+

GearHead71
GearHead71

You are correct, the RAM had an 8 speed.  it definitely feels like the 6 speed in the GMC could use at least one more gear.  Trying to maintain 55 mph up a hill you are either screaming in one gear or

dieselfan1
dieselfan1

For me, Ford is not an option. No thanks.

GearHead71 Enthusiast

GearHead71

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4 minutes ago, Ray Pickle said:

I can only guess there is a powertrain issue in your truck. This truck would benefit from a deeper axle ratio, but in my personal experience I have not had ANY problems maintaining 55 up any pass I have been on. That includes numerous passes through the continental divide. I will admit that I will typically pull a grade like the Eisenhower tunnel pass at 40 to 45 mph just because it is easier on the truck and therefore my wallet. That being said those grades are the rare exception both in grade and elevation. 

Heading eastbound up to Eisenhower is definitely one spot I can't maintain 55mph.  Maybe I just need to learn patience and take it at 45.  Haha. 

 

But that was the spot where it was embarrassing.  My father in law passed me in his 2014 Tundra and my buddy passed me in his 2019 Ram 1500 (we all have similar weight trailers).  I was the only one that couldn't maintain the speed limit in my brand new "big" truck.  

Ray Pickle Enthusiast

Ray Pickle

Posted
Posted

As someone has already mentioned , big boy truck weighs 7k empty.  There is more to competent towing than how fast you can pull a 7% grade at 11k ft. I guarantee you my gasser will pull my 5th wheel up the "ike" faster than astock Tundra or 1500 5.7! Clearly neither of those vehicles should even attempt but?

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GearHead71 Enthusiast

GearHead71

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Posted (edited)

So just to have some hard numbers to look at I looked up the gearing for the 6 Speed:

 

Gear Gear Ratio
1st 4.03
2nd 2.36
3rd 1.53
4th 1.15
5th 8.5
6th 0.67

 

Other stats:

Front and Rear Gear Ratio: 3.73:1

Engine Redline: 5600RPM

Max Torque:  464 @ 4000RPM

Max HP: 401 @ 5200PRM

Tire Size: 265/70R17 (without actually measuring my tires, that's about a 99.3 inch circumference)

 

Given this, here are the engine RPMs at 3 different MPH (RPMs in bold are above redline):

 

55MPH:

Gear Engine RPM
1st 8794.345637
2nd 5150.038636
3rd 3338.796234
4th 2509.552725
5th 1854.886797
6th 1462.08724

 

60MPH:

Gear Engine RPM
1st 9593.831604
2nd 5618.223966
3rd 3642.323165
4th 2737.693882
5th 2023.512869
6th 1595.004262


65MPH:

Gear Engine RPM
1st 10393.31757
2nd 6086.409297
3rd 3945.850095
4th 2965.835039
5th 2192.138942
6th 1727.921283

 

As you can see (take the trailer out of the equation), at 60MPH the LOWEST gear I can use is 3rd and the RPMs are only at 3642.  That's a little below where the max torque is, and well below max hp.  I'm going to play around with what re-gearing will look like (either 4.10 or 4.56).

 

Take even 55MPH.  Your options are either almost 5200 RPM (screaming) or 3340 (no power).  This is exactly what I've been experiencing. 

 

To me, it still seems like it's missing a gear between 2nd and 3rd.  Either that, or maybe they should have "shortened" the gap between 2nd and 3rd.  At 60 MPH it's a 2,000 RPM jump between 2nd and 3rd (even though you can't use 2nd gear) but only a 900 RPM jump between 3rd and 4th; 715RPM between 4th and 5th.  I know those shouldn't be linear, but still seems like a big gap.

Edited by GearHead71
GearHead71 Enthusiast

GearHead71

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Posted (edited)
1 hour ago, Ray Pickle said:

As someone has already mentioned , big boy truck weighs 7k empty.  There is more to competent towing than how fast you can pull a 7% grade at 11k ft. I guarantee you my gasser will pull my 5th wheel up the "ike" faster than astock Tundra or 1500 5.7! Clearly neither of those vehicles should even attempt but?

I'm with you!  And I LOVE the truck and the towing other than this one issue.  Unfortunately for me, the times it struggles and can't maintain the speed limit kill the rest of the experience.  Maybe a re-gear will help me, or maybe I just need to get over this one instance of under-performance (that would be cheaper haha) 

Edited by GearHead71
Ray Pickle Enthusiast

Ray Pickle

Posted
Posted

If your truck is 2wd rear gearing is reasonable.  I would put 4:10 in mine if it was 2wd. Not going to invest in 2 gearsets for the improvement in the occasional steep mountain towing I do. Probably worth it if you live in that area and tow heavy often through that terrain.

GearHead71 Enthusiast

GearHead71

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Posted
10 minutes ago, Ray Pickle said:

If your truck is 2wd rear gearing is reasonable.  I would put 4:10 in mine if it was 2wd. Not going to invest in 2 gearsets for the improvement in the occasional steep mountain towing I do. Probably worth it if you live in that area and tow heavy often through that terrain.

Mine is 4WD.  We tow in the mountains about 6 times a year.  The only thing that makes me nervous is I'm only towing 5500lbs.  I bought this truck so we could get a bigger camper (around 9500lbs).  Given how it struggles now in the mountains, I'm not sure how much worse it will do with the larger camper.

 

I'm going to call around and see how much a re-gear is.  Also, not sure the jump to 4.10 would be enough of a difference.  Might need to go up to 4.56 and at that point you need a new carrier as well...

kenny_r Enthusiast

kenny_r

Posted
Posted

I have a 2017 6.0 and to me it seems like it will pull all day long at 3500rpm. I’m usually loaded around 8k traveling up to 7k ft elevation. I wanna say I’m locked into 4th.[emoji848]

ShotgunZ71 Senior Enthusiast

ShotgunZ71

Posted
Posted

Most of the time, if I'm in rolling hills or mountainous area, I'll lock out 5th and 6th on the interstate to keep the RPM above 3000. If the highway speed is slow enough, I'll lock out 4th as well. I just like to stay in the 3-4k range when going up and down inclines, so the speed doesn't vary so much and also so that you have a bit better engine braking. I've not had any issue with my truck and camper getting up to speed on any grade yet. That's pulling a 42', 14.5k lb 5th wheel, also.

 

However, I will say that if I encounter a normal driving situation (grade or otherwise)where the truck will not maintain speed or even attempt to maintain or gain speed, I will absolutely look at other options. Those will likely be a Ford with the 7.3 gas engine or a diesel, be it Duramax or Powerstroke. 

 

I feel that there is something amiss with the OP's truck or programming, etc. The truck should in no way struggle up that grade with that light of a load. Something doesn't make sense, especially since the truck has performed that poorly multiple times for him.

Colossus Senior Enthusiast

Colossus

Posted
Posted

So is the performance the same with what the OP encountered as well as with what that truck video group that tests the trucks?  6.6 just sucks in the mountains? 

KARNUT Senior Enthusiast

KARNUT

Posted
Posted

When I was pulling back in the day up to the late 90s, some in the early 2000s. The HP and TQ was around 165-200 and low 400 in diesel. You had one transmission gear choice after 45 mph shift to one to one or 4th gear or drive in auto. Usually 410 gear. Gas engines depending on gearing, I ran 410. I could downshift even at 60. Gas engines could be had with 300HP around 400 TQ. I used 3/4 ton at that time Ram V-10. My trailer along was 7500 lbs.
Maintaining HWY speed in drive or 4TH with a stick wasn’t a problem at 3K RPMs. I was left with one gear to down shift when needing. As soon as I lost speed on a hill I did that and maintained speed. Seems there’s either a know how problem or a gearing problem. I would want 3K at 60 in a drive gear not over drive. With the gear spacing you should be able to have over drive empty driving. And two gears for hill pulling and maintaining speed. Remember my trailer was 7500lbs. My tractor was 14K more and had a cab. I can’t believe GM would miss the boat that bad. Something’s amiss.


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GearHead71 Enthusiast

GearHead71

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17 minutes ago, KARNUT said:

When I was pulling back in the day up to the late 90s, some in the early 2000s. The HP and TQ was around 165-200 and low 400 in diesel. You had one transmission gear choice after 45 mph shift to one to one or 4th gear or drive in auto. Usually 410 gear. Gas engines depending on gearing, I ran 410. I could downshift even at 60. Gas engines could be had with 300HP around 400 TQ. I used 3/4 ton at that time Ram V-10. My trailer along was 7500 lbs.
Maintaining HWY speed in drive or 4TH with a stick wasn’t a problem at 3K RPMs. I was left with one gear to down shift when needing. As soon as I lost speed on a hill I did that and maintained speed. Seems there’s either a know how problem or a gearing problem. I would want 3K at 60 in a drive gear not over drive. With the gear spacing you should be able to have over drive empty driving. And two gears for hill pulling and maintaining speed. Remember my trailer was 7500lbs. My tractor was 14K more and had a cab. I can’t believe GM would miss the boat that bad. Something’s amiss.


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I really hope something is amiss. I love this truck otherwise but this is really making me regret my decision. I'm not a Ford guy but looking at the 7.3 gas with the 10 speed is making me wonder. 

 

I really think if my truck had the 10 speed I wouldn't be having this problem. It just needs a gear between second and third to bring the engine RPMs back near the power band at 60 miles an hour

KARNUT Senior Enthusiast

KARNUT

Posted
Posted
I really hope something is amiss. I love this truck otherwise but this is really making me regret my decision. I'm not a Ford guy but looking at the 7.3 gas with the 10 speed is making me wonder. 
 
I really think if my truck had the 10 speed I wouldn't be having this problem. It just needs a gear between second and third to bring the engine RPMs back near the power band at 60 miles an hour

I hear you. I definitely wasn’t a Ram guy when I had my V-10. Diesels at the time didn’t have enough gear spacing for downshifting on hills. You had to be at 45 mph before going down to 3rd gear. The gas could go at 60. I was pulling pretty heavy. My V-10 had no problem pulling my empty 7500lb trailer in 5th overdrive. It was 300hp 400 ft lbs of TQ. It had a 355 gear. Our auto V-10 had 410. My Cummings diesels had 355. My gear spacing on the diesel was 45 in third 60 in fourth 92 in over drive. Maintaining speed in the diesel was harder than the V-10. Different game now.


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Ray Pickle Enthusiast

Ray Pickle

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Posted

Again TFL tests require they do no manual shifting for the sake of uniformity. I would make a significant bet the g.m. and Ford would be within 30 sec. Going up the Ike if both where maually shifted  to their best advantage. If the Ford was equipped with standard 3.55 I believe it would be behind. What their test does prove is that Ford has been less conservative in their tuning choices relating to shift strategies. The 2 engines are nearly identical in torque from 2800 rpm up to over 4500 rpm. In spite of the significant displacement differences. The G.M. gets better mileage and  the Ford with optional 7.3 and optional 4.30 pulls a little better. The 10 speed transmission is an advantage, but on a gasser with a 1k to 6k operating range, not as significant as for a diesel .

GearHead71 Enthusiast

GearHead71

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I did the same exercise for the Ford 7.3 (w/ 3.55 and 4.30) as well as the RAM with the 6.4 (3.73 and 4.10).  I know I'm only looking at one specific speed range (55-65MPH) but that's where mine is struggling.  What you can see from the data below is at 60MPH both the RAM and Ford (in BOTH axle gear options) have a gear (or TWO) in the 4000-5000 RPM range whereas the GMC does not.  (I had a hard time finding redline for the RAM 6.4L hemi with the 8HP75 trans as well as the for Ford 7.3 with the 10R140, but this will get us close enough).

 

RAM 2500 6.4L Hemi (redline: 5800 RPM)
Diff Gears 3.73        
      55 MPH 60 MPH 65 MPH
Gear Gear Ratio Final Drive Engine RPM Engine RPM Engine RPM
1st 4.71 17.5683 9782.917 10672.27 11561.63
2nd 3.14 11.7122 6521.945 7114.849 7707.753
3rd 2.1 7.833 4361.81 4758.339 5154.867
4th 1.66 6.1918 3447.907 3761.353 4074.799
5th 1.28 4.7744 2658.627 2900.321 3142.014
6th 1 3.73 2077.053 2265.876 2454.698
7th 0.83 3.0959 1723.954 1880.677 2037.4
8th 0.66 2.4618 1370.855 1495.478 1620.101

 

RAM 2500 6.4L Hemi (redline: 5800 RPM)
Diff Gears 4.1        
      55 MPH 60 MPH 65 MPH
Gear Gear Ratio Final Drive Engine RPM Engine RPM Engine RPM
1st 4.71 19.311 10753.34 11730.92 12708.49
2nd 3.14 12.874 7168.894 7820.612 8472.329
3rd 2.1 8.61 4794.483 5230.345 5666.207
4th 1.66 6.806 3789.925 4134.463 4479.002
5th 1.28 5.248 2922.352 3188.02 3453.688
6th 1 4.1 2283.087 2490.641 2698.194
7th 0.83 3.403 1894.962 2067.232 2239.501
8th 0.66 2.706 1506.838 1643.823 1780.808

 

Ford F250 7.3L Gas (redline: 5500 RPM)
Diff Gears 3.55        
      55 MPH 60 MPH 65 MPH
Gear Gear Ratio Final Drive Engine RPM Engine RPM Engine RPM
1st 4.615  16.38325 9123.022 9952.387 10781.75
2nd 2.929 10.39795 5790.104 6316.477 6842.85
3rd 2.132 7.5686 4214.579 4597.723 4980.866
4th 1.773 6.29415 3504.901 3823.528 4142.156
5th 1.519 5.39245 3002.789 3275.77 3548.75
6th 1.277 4.53335 2524.398 2753.889 2983.38
7th 1 3.55 1976.819 2156.53 2336.241
8th 0.85 3.0175 1680.297 1833.051 1985.805
9th 0.687 2.43885 1358.075 1481.536 1604.998
10th 0.632 2.2436 1249.35 1362.927 1476.504

 

Ford F250 7.3L Gas (redline: 5500 RPM)
Diff Gears 4.3        
      55 MPH 60 MPH 65 MPH
Gear Gear Ratio Final Drive Engine RPM Engine RPM Engine RPM
1st 4.615 19.8445 11050.42 12055 13059.59
2nd 2.929 12.5947 7013.366 7650.944 8288.523
3rd 2.132 9.1676 5104.983 5569.072 6033.162
4th 1.773 7.6239 4245.373 4631.316 5017.259
5th 1.519 6.5317 3637.181 3967.834 4298.486
6th 1.277 5.4911 3057.722 3335.697 3613.672
7th 1 4.3 2394.457 2612.135 2829.813
8th 0.85 3.655 2035.289 2220.315 2405.341
9th 0.687 2.9541 1644.992 1794.537 1944.082
10th 0.632 2.7176 1513.297 1650.87 1788.442

 

GMC 2500 6.6L Gas (redline: 5600 RPM)
Diff Gears 3.73        
      55 MPH 60 MPH 65 MPH
Gear

Gear

Ratio

Final

Drive

Engine

RPM

Engine

RPM

Engine

RPM

1st 4.03 15.0319 8794.729042 9594.25 10393.77
2nd 2.36 8.8028 5150.263161 5618.469 6086.675
3rd 1.53 5.7069 3338.941795 3642.482 3946.022
4th 1.15 4.2895 2509.662134 2737.813 2965.964
5th 0.85 3.1705 1854.967664 2023.601 2192.235
6th 0.67 2.4991 1462.150982 1595.074 1727.997

 

 

I did look at what would happen if I re-geared to 4.56 (4.10 wouldn't be a big enough change) and that would get me from being stuck at 3600 RPM at 60 MPH with no power to 4450 RPM which is closer to the max torque.  I feel like that would solve my problem but my gas mileage would take a hit (this is also my daily driver) and I need to look and make sure I'm not just moving this problem to a different gear/speed range.

 

 

GMC 2500 6.6L Gas (redline: 5600 RPM)
Diff Gears 4.56        
      55 MPH 60 MPH 65 MPH
Gear

Gear

Ratio

Final

Drive

Engine

RPM

Engine

RPM

Engine

RPM

1st 4.03 18.3768 10751.73309 11729.16 12706.59
2nd 2.36 10.7616 6296.300272 6868.691 7441.082
3rd 1.53 6.9768 4081.923481 4453.007 4824.091
4th 1.15 5.244 3068.112421 3347.032 3625.951
5th 0.85 3.876 2267.735267 2473.893 2680.051
6th 0.67 3.0552 1787.508976 1950.01 2112.511

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