Pros and Cons of Installing Later Transmission Thermostat with Lower Opening Temperature

64BAwagon · December 18, 2022

I use tow haul whenever I have a trailer on, especially this 12k fifth wheel.

I am assuming its 6th gear but its impossible to know since there isnt any indicator on the dash as to what gear its in. I wasnt aware that 6th got locked out in Tow/haul. I was assuming it was because the RPM's drop to 1500 at 64 Mph.

There isnt any mention of the lock out in the HD manual. The only mention of it i can see anywhere is on 1500's

Just for the sake of argument I have towed several different trailers with my trucks over the years, two of them were over 10k and I have probably logged well over 30k miles towing them. I am quite familiar with towing.

Edited December 19, 2022 by 64BAwagon

Jettech1 · December 19, 2022

1 hour ago, 64BAwagon said:

I use tow haul whenever I have a trailer on, especially this 12k fifth wheel.

I am assuming its 6th gear but its impossible to know since there isnt any indicator on the dash as to what gear its in. I wasnt aware that 6th got locked out in Tow/haul. I was assuming it was because the RPM's drop to 1500 at 64 Mph.

There isnt any mention of the lock out in the HD manual. The only mention of it i can see anywhere is on 1500's

Just for the sake of argument I have towed several different trailers with my trucks over the years, two of them were over 10k and I have probably logged well over 30k miles towing them. I am quite familiar with towing.

Just drop the shifter into manual and it will show what gear it's in bottom right of your speedometer screen. Our camper is only 8klbs but yes, the tow/haul mode does lock out 6th gear. And with tow/haul mode on your rpms at 64 should be around 2100 not 1500. 1500rpm is 6th gear. And from the picture you posted I see you are a Grand Design owner too. We have a 2023 Grand Design Imagine 2800BH. LOVE IT!!!

Edited December 19, 2022 by Jettech1

64BAwagon · December 19, 2022

Not sure where youre info comes from but on my truck T/H does not lock out 6th gear. I wish it would though. I dont want it in 6th because it just doesnt have the torque. The sweet spot seems to be a little over 2000 rpms which is where 5th puts me at 64. I do notice that above 66 mph or so it tries to shift into 6th even more.

This 337RLS is our 2nd GD trailer, the first was a 2600RB that I pulled with a 1/2 ton double cab 5.3, It was definitely the top of the size I would tow with that truck

Jettech1 · December 19, 2022

22 minutes ago, 64BAwagon said:

Not sure where youre info comes from but on my truck T/H does not lock out 6th gear. I wish it would though. I dont want it in 6th because it just doesnt have the torque. The sweet spot seems to be a little over 2000 rpms which is where 5th puts me at 64. I do notice that above 66 mph or so it tries to shift into 6th even more.

This 337RLS is our 2nd GD trailer, the first was a 2600RB that I pulled with a 1/2 ton double cab 5.3, It was definitely the top of the size I would tow with that truck

Perhaps the 3500's don't do that. My information comes from personal experience with my 2500.

Ray Pickle · December 19, 2022

I have a 20' 2500 and it does not lock out 6th gear. In tow/haul it rarely upshifts to 6th gear but it will under low load with speeds of 60 plus mph, "slight downhill", also agree that 5th is preferred cruising gear and the one that truck stays in on relatively level ground.

Another JR · December 19, 2022

I can’t imagine they have different transmission programming for 2500 vs 3500.

Jettech1 · December 20, 2022

11 hours ago, Another JR said:

I can’t imagine they have different transmission programming for 2500 vs 3500.

I looked everywhere today and couldn't find it. I did read something about 6 months ago that said the 3500 gassers are not torque limited from take-off whereas the 2500's are. I can't find it for the life of me but I do remember reading that somewhere. I'll keep searching.

Another JR · December 20, 2022

1 hour ago, Jettech1 said:

I looked everywhere today and couldn't find it. I did read something about 6 months ago that said the 3500 gassers are not torque limited from take-off whereas the 2500's are. I can't find it for the life of me but I do remember reading that somewhere. I'll keep searching.

I think i remember reading that about the diesel.

Jettech1 · December 20, 2022

8 hours ago, Another JR said:

I think i remember reading that about the diesel.

You're probably right. I did several months of intense research before I bought my truck at the end of August, so much that a lot of info got jumbled around. I do know for a fact that my 2022 2500 gasser, in tow/haul mode locks out 6th gear. The only other plausible explanation is that it was an update on the later build trucks.

Pryme · December 20, 2022

3 hours ago, Jettech1 said:

You're probably right. I did several months of intense research before I bought my truck at the end of August, so much that a lot of info got jumbled around. I do know for a fact that my 2022 2500 gasser, in tow/haul mode locks out 6th gear. The only other plausible explanation is that it was an update on the later build trucks.

Mine was built in July 22 same as yours I believe so I’ll have to try tow haul and see what happens.

Edited December 20, 2022 by Pryme

Jettech1 · December 21, 2022

9 hours ago, Pryme said:

Mine was built in July 22 same as yours I believe so I’ll have to try tow haul and see what happens.

I tried it today unloaded on the highway. Was going 65mph, rpms were at 1500. Turned the TH mode knob, truck immediately downshifted into 5th gear, 2000rpms and stayed there. It would not go into 6th gear. It appears I made a bad assumption that the prior model years do that too. To me that would suck while towing with the trans. constantly seeking out 6th gear in TH mode. Too much shifting, and the only way to stop that would be to drop the shifter into manual mode and do it yourself. And that would suck too because when the truck slows down up a long grade you would have to manually hit the switch to downshift into 4th gear, then manually make it go back into 5th. That's too much BS in my opinion. I'm hoping there's an update for those earlier model years. That would drive me nuts when towing. 5th gear, 2000rpms is the sweet spot for towing and letting the trans. just do it's thing up and down grades and not going into 6th.

Another JR · December 21, 2022

19 minutes ago, Jettech1 said:

I tried it today unloaded on the highway. Was going 65mph, rpms were at 1500. Turned the TH mode knob, truck immediately downshifted into 5th gear, 2000rpms and stayed there. It would not go into 6th gear. It appears I made a bad assumption that the prior model years do that too. To me that would suck while towing with the trans. constantly seeking out 6th gear in TH mode. Too much shifting, and the only way to stop that would be to drop the shifter into manual mode and do it yourself. And that would suck too because when the truck slows down up a long grade you would have to manually hit the switch to downshift into 4th gear, then manually make it go back into 5th. That's too much BS in my opinion. I'm hoping there's an update for those earlier model years. That would drive me nuts when towing. 5th gear, 2000rpms is the sweet spot for towing and letting the trans. just do it's thing up and down grades and not going into 6th.

That’s not how the transmission works in “L.” The transmission shifts normally otherwise but will not upshift beyond the selected gear. For example, in L4, it will use 1, 2, 3, and 4, but won’t shift to 5 and 6.

Jettech1 · December 21, 2022

5 minutes ago, Another JR said:

That’s not how the transmission works in “L.” The transmission shifts normally otherwise but will not upshift beyond the selected gear. For example, in L4, it will use 1, 2, 3, and 4, but won’t shift to 5 and 6.

That's good to know. So if it's in say 5th in L mode it will auto downshift into 4th if needed then go back to 5th on it's own? If so that's a lot better than what I thought. I was thinking you would have to pay total attention to what gear you're in when in L mode. Great information, thank you!!

Another JR · December 21, 2022

22 minutes ago, Jettech1 said:

That's good to know. So if it's in say 5th in L mode it will auto downshift into 4th if needed then go back to 5th on it's own? If so that's a lot better than what I thought. I was thinking you would have to pay total attention to what gear you're in when in L mode. Great information, thank you!!

Correct. It’s not a manual mode. It is a selectable top gear mode. The transmission will shift normally except it won’t upshift beyond your selection. It can be used in normal or tow/haul mode.

KARNUT · December 21, 2022

7 hours ago, Another JR said:

Correct. It’s not a manual mode. It is a selectable top gear mode. The transmission will shift normally except it won’t upshift beyond your selection. It can be used in normal or tow/haul mode.

Well it’s manual mode with the added feature. If you put it second gear and it hits the rev limit. It’s in manual mode.