When pulling my TT (around 6,500 pounds) I like using T/H for going down hills (lots of them in BC) but end up turning it off as I don't really need the higher shift points for this size a trailer. In T/H the truck takes a while to get into 5th but without the T/H it pulls just fine in 5th.

Is this something that can be reprogramed? Can shift points be set at all? I know I'm probably going the opposite way of what most people do but I want to help towing economy and don't need to be going 100kmh in 4th.

Do a search on "tow / haul;" lots of information available.

To answer your question, the torque converter lock-up function works differently in normal and tow / haul modes. IIRC, the torque converter locks up earlier in fifth gear in tow / haul. Maybe some of our transmission guys will comment. :)

I use my tow / haul the same way you do... I don't use it when towing the boat (3,500 lbs.), but it's invaluable when towing the 5'ver (14,000 lbs.).

I would (and do) just continue to run it like you do now. Staying in T/H will only hurt your mileage.

I use T/H whenever I'm towing anything. I find the trans runs much cooler that way. You can "trick" the Allison into up shifting into 5th sooner by dropping out of T/H momentarily until it shifts then reengaging it. That will resolve the issue of running around in 4th. Mine, at least, will stay in 5th to just about 50 mph before downshifting.

TC

My understanding is that the shift points are at a HIGHER rpm in T/H, but the torque converter lockup is at a LOWER rpm, and it's a more deliberate lockup (doesn't "slide" comfortably into lockup).

If that's true, and you are driving around in normal mode in O/D at too low of a rpm, you may be slipping your torque converter under moderate loads, which isn't good. It's probably why the trans runs cooler in T/H.

I like the idea of dropping out of T/H momentarily until the trans shifts to O/D, then switching back to T/H so your torque converter locks up at lower rpm.

Again, it's only my understanding.

I use T/H whenever I'm towing anything. I find the trans runs much cooler that way. You can "trick" the Allison into up shifting into 5th sooner by dropping out of T/H momentarily until it shifts then reengaging it. That will resolve the issue of running around in 4th. Mine, at least, will stay in 5th to just about 50 mph before downshifting.

TC
This is what I do also.

The short answer is No. No one has made a breakout box for reprogramming an Allison.

Personally, I would just do what you do. or leave it in Normal mode. I use the T/H mode for grad braking and in town driving with the trailer.

As for Lockup of the converter when at highway speeds, whether you are in T/H mode or normal, it won't matter. The converter will be locked up unless you put your foot into the injectors.

Normally, on a hot day, I will start out in T/H then once at the speed I'm going cruise at, shift back to normal mode. I have not seen a high temp in the tranny using this method. (I have not seen a high temp in the tranny using any method for that matter.)

IT's easier on the engine to pull at certain rpms. The tow haul is supposed keep the truck optimal for pulling a load. Just go a little faster until it shifts.

The short answer is No. No one has made a breakout box for reprogramming an Allison.

Ummm.... EFILive... Not a breakout box but it can reprogam the TCM.

I use T/H whenever I'm towing anything. I find the trans runs much cooler that way. You can "trick" the Allison into up shifting into 5th sooner by dropping out of T/H momentarily until it shifts then reengaging it. That will resolve the issue of running around in 4th. Mine, at least, will stay in 5th to just about 50 mph before downshifting.

TC

I just hauled a suburban yesterday. Was nothing for tts in reg. or tow mode. I did exactly what you did w/ the t/h and kept the co-pilot on intermediate.

As Cougar281 said, EFILive will allow you to program all the shift points and also the TCC lock-up speeds. There is over 100 tables and parameters you can change in the TCM, this is not 'fooling' the TCM, you are changing the TCM's calibrations.

Cheers,
Ross

So I'll keep doing what I'm doing and not worry about it.

Thanks.

Thanks Ross, I stand corrected. I've not kept up on the tech.

Uh, why yes you can change all you want in the TCM with EFILive. However, I would be very careful when playing with the parameters of the ECM and the TCM. The uniniated can turn those items into junk if restraint is not used.