Heavy Haul Review

Jon A · June 11, 2014

Could you guys note what speed/RPM/gear (two of the three) you noticed this issue the most? That would be good data for future reference.

Anyway, the tow/haul mode is supposed to hold gears longer to prevent hunting while towing, so it's not the idea that's wrong. In looking at the programming, it looks to me like they just took the idea a bit too far. Some examples:

In Tow/Haul mode (using a 3.42 5.3 for example) if you're going slower than 37 MPH it will never shift into 4th even if you let off the throttle completely. In Drive it'll shift into 4th as low as 24 MPH under light throttle.

In T/H mode if you're going slower than 50 MPH it will never shift into 5th. In D it'll shift into 5th as low as 32 MPH under light throttle.

In T/H mode if you're going slower than 67 MPH it will never shift into 6th. In D it'll shift into 6th as low as 42 MPH under light throttle.

So as you can see, those differences are pretty extreme. It's the right idea, I think they just took it a bit too far. Simply knocking down those MPH numbers in T/H mode a bit (maybe splitting the difference, maybe a bit less than that) would probably make for a very good T/H mode. Interestingly, the 6.2 and 5.3 programming in these tables is very similar.

Now, the issue they had on TFL Truck with the 6.2, was completely different. That was under WOT (where you want it to hold the gear all the way until redline), and they had the opposite problem--it wouldn't hold 2nd long enough.

The 6.2 in T/H mode will not downshift from 3rd into 2nd, even with your foot to the floor, until you slow down to below 46 MPH. In Drive, it'll downshift if you put your foot to the floor as high as 54 MPH. The 6.2 clearly has the power to easily accelerate any legal load up pretty much any hill in 2nd, the problem is in T/H mode it "shortshifts" out of 2nd, back into 3rd at 5200 RPM. If left in drive, it'll scream all the way to 5800 RPM. Why GM did this exactly, we'll probably never know--better mileage? Maybe a bigger margin of safety for the cooling system in the SAE desert hillclimb test? Better longevity? Maybe they were just clueless?

Regardless, for those of you who watched the test in detail, given the above it's obvious the Chevy would have been dramatically faster if simply left in "Drive." If held in 2nd in manual mode of course they could have kept it above 60 MPH very easily the whole way up (watch the older Ford Superduty 6.2 test and it basically does just that--holds 2nd gear all the way up).

I know the risk of losing the warranty is pretty scary, but all these problems can easily be fixed very cheaply with a tune.

nards444 · June 11, 2014

Could you guys note what speed/RPM/gear (two of the three) you noticed this issue the most? That would be good data for future reference.

Anyway, the tow/haul mode is supposed to hold gears longer to prevent hunting while towing, so it's not the idea that's wrong. In looking at the programming, it looks to me like they just took the idea a bit too far. Some examples:

In Tow/Haul mode (using a 3.42 5.3 for example) if you're going slower than 37 MPH it will never shift into 4th even if you let off the throttle completely. In Drive it'll shift into 4th as low as 24 MPH under light throttle.

In T/H mode if you're going slower than 50 MPH it will never shift into 5th. In D it'll shift into 5th as low as 32 MPH under light throttle.

In T/H mode if you're going slower than 67 MPH it will never shift into 6th. In D it'll shift into 6th as low as 42 MPH under light throttle.

So as you can see, those differences are pretty extreme. It's the right idea, I think they just took it a bit too far. Simply knocking down those MPH numbers in T/H mode a bit (maybe splitting the difference, maybe a bit less than that) would probably make for a very good T/H mode. Interestingly, the 6.2 and 5.3 programming in these tables is very similar.

Now, the issue they had on TFL Truck with the 6.2, was completely different. That was under WOT (where you want it to hold the gear all the way until redline), and they had the opposite problem--it wouldn't hold 2nd long enough.

The 6.2 in T/H mode will not downshift from 3rd into 2nd, even with your foot to the floor, until you slow down to below 46 MPH. In Drive, it'll downshift if you put your foot to the floor as high as 54 MPH. The 6.2 clearly has the power to easily accelerate any legal load up pretty much any hill in 2nd, the problem is in T/H mode it "shortshifts" out of 2nd, back into 3rd at 5200 RPM. If left in drive, it'll scream all the way to 5800 RPM. Why GM did this exactly, we'll probably never know--better mileage? Maybe a bigger margin of safety for the cooling system in the SAE desert hillclimb test? Better longevity? Maybe they were just clueless?

Regardless, for those of you who watched the test in detail, given the above it's obvious the Chevy would have been dramatically faster if simply left in "Drive." If held in 2nd in manual mode of course they could have kept it above 60 MPH very easily the whole way up (watch the older Ford Superduty 6.2 test and it basically does just that--holds 2nd gear all the way up).

I know the risk of losing the warranty is pretty scary, but all these problems can easily be fixed very cheaply with a tune.

Next time I take it out Ill try to pay better attention to the specifics. Most of the problem was under 50mph, and I would tend to think the problem gears were probably 3-5. But no I agree the right idea is there, but execution sucked.

Jon A · June 11, 2014

Yeah, it just needs a few tweaks. I actually like the 1-2 shift in T/H at low speed (“parking lot speeds”) light throttle better even in normal driving. The stock Drive mode shifts into 2^nd really early and makes the engine fall on it’s face a bit. The higher 1-2 shift improves driveability IMHO. But obviously holding the higher gears so long gets tiresome.

In looking at the numbers above, it really looks like somebody picked a spot on a line on a chart right at 1600 RPM and decided not to let the engine get below that in T/H even under light throttle, for whatever reason. In Drive they let it go all the way down to 1050 RPM in light cruise. I'm thinking lowering that to around 1400 or so in the higher gears in T/H would be a big improvement.

nards444 · June 11, 2014

Yeah, it just needs a few tweaks. I actually like the 1-2 shift in T/H at low speed (“parking lot speeds”) light throttle better even in normal driving. The stock Drive mode shifts into 2^nd really early and makes the engine fall on it’s face a bit. The higher 1-2 shift improves driveability IMHO. But obviously holding the higher gears so long gets tiresome.

In looking at the numbers above, it really looks like somebody picked a spot on a line on a chart right at 1600 RPM and decided not to let the engine get below that in T/H even under light throttle, for whatever reason. In Drive they let it go all the way down to 1050 RPM in light cruise. I'm thinking lowering that to around 1400 or so in the higher gears in T/H would be a big improvement.

Shifting from 1-2 isnt an issue it just seems anything past that. But like you said I think a point on a line was chosen and they went with that. Or they figured on most guys tow x weight and figured out how the truck behaves towing that weight and went with set points. So instead of the system learning or reacting its just doing a pre-programmed flight path so to speak. If thats true then guys like me who have the max tow (which who buys that just for fun) were short changed.

calgator73 · June 29, 2014

All,

I just picked up my 2014 chevy 6.2L with Max Towing and I'm possibly pushing the tongue weight limit without a weight distribution hitch. I didn't consider reviewing the other data as I just looked at total towing capacity, since I have 3/4 duramax which doesn't need a weight distribution.

My boat (25')/trailer is around 8000 calculated weight and I need to get the boat to a scale to determine actual weight. If you figure 10% tongue weight I'm OK (at 800) but if it is 15% I'm at 1200 lbs. I was hoping to stay away from a weight distribution hitch because I tractor lauch in Alaska. You dismount the boat and a tractor connects and pushes the trailer/boat into the ocean. I wouldn't like to disconnect the weight distribution system every time I tractor launch plus I don't know how it would connect to boat trailer.

Any help would be appreciated. I thought with the max towing package it would be higher tongue weights which is my fubar!

Ryan

I have the same issue. Hitch provided is a class 4. They provide the 1200 TW to help arrive at 12K trailer weight. Problem is that it's based on 10% tw which precludes you from towing heavier trailers with higher percentage tw. My travel trailer weighs 9390 dry and has a dry tw of 1175. Once loaded my tongue should be ~1300. Check out curt mfg. #15323... Only issue is the hitch cross member will be exposed.

calgator73 · June 30, 2014

I have the same issue. Hitch provided is a class 4. They provide the 1200 TW to help arrive at 12K trailer weight. Problem is that it's based on 10% tw which precludes you from towing heavier trailers with higher percentage tw. My travel trailer weighs 9390 dry and has a dry tw of 1175. Once loaded my tongue should be ~1300. Check out curt mfg. #15323... Only issue is the hitch cross member will be exposed.

Spoke with representative from etrailer. By replacing the class IV hitch with a V one weak spot is removed. Next limit impacting tw is rgawr.

calgator73 · July 13, 2014

Here's the hitch installed.

bogeypro · July 13, 2014

I regularly tow a 6000lb boat. I dont use tow haul mode. Holds shifts way too long and diwnshifts are too harsh. Never had a problem using regular mode while towing.

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