not sure never driven an truck with an allison. on my previous truck an 06 6.0 80e combo as well same tuner, i clicked the tow haul, truck would down shift and had higher shift points etc. as set in hptuners. but with this newer ecm/tcm combo, same tuner can't get it to downshift. truck shifts at tow haul rpms but doesn't down shift when the button is pressed

 

That's because it's not supposed to downshift simply by touching the button. Change the shift points in the tow/haul tables to some outlandish numbers if you want to see a downshift. All the button does is make the truck prefer to hold gears longer and be more aggressive about unlocking the torque converter.

 

If you can see the shift speed tables in your tune you'll understand that a downshift is not a given every time you push that button. It all depends on where the shift points are programmed and at what speed you are cruising at. Based on speed and throttle positions, sometimes it will and sometimes it won't.

Raise your shift speeds in tow/haul and you'll get more of what you're looking for.

 

maybe this will help you guys understand what i mean, video ain't mine. just found it online.
notice how when he clicks the tow haul cruising at 30, it downshifts so he gets a jump when he floors it and not the lag you get when in D. check it out. heres the link: Silverado tow haul tune - YouTube

on mine, when i press tow haul, the light comes up but does absolutely nothing

 

That's because he set his shift points set so damn high that it's not driveable.

Tell your tuner what you want in your tow/haul tune is undriveably high shift points. I think he will understand what you're trying to do, then.

Also, I have you checked to see if GM implemented the advanced abuse mode? That would also prevent the TCM from allowing those high shift points.

 

If you don't want to wait for a downshift, simply pull the gear selector out of overdrive until you get the engine revs you wish. Then once you get on the throttle, shift back into OD and let the trans upshift as it would

Simply pushing the t/h button will not cause a downshift with normal settings.

peace
Hog