2016 2500 HD trans doesn't shift up when towing

SierraHD17 · June 4, 2019

On 5/28/2019 at 9:59 PM, Jak860 said:

I know this is an old thread but I just experienced the same problem as the original post. I have a 2105 Silverado 2500HD 6.0, 6 speed automatic, 36000 miles. I was towing my loaded toy hauler that weighs in at roughly 10,000lbs. While climbing a long grade in manual 5th in tow haul mode the truck eventually slowed to under 40 mph in 3rd gear then shifted automatically into 2nd at 4200 rpm. Once the grade started to taper off I backed off on the throttle and expected an upshift into 3rd but it never came. Instead it stayed in 2nd even on the level with my foot completely off the gas. The only way I could get it to upshift is to move the selector up into neutral while coasting and then put it into drive range. It would then go into a higher gear. Several times when I tried to place it back into manual 5th it would drop all the way back into 2nd with high rpms. Then after driving awhile longer in drive range all went back to normal until it had to drop back into second while climbing a grade. It did this several times over 300 miles. I used to build and repair transmissions years ago. It acts like a stuck governor valve did way back when. I'm a little concerned about taking it to my local dealer as they don't seem to have the expertise or even the concern to a problem that is out of the ordinary. I have canvassed the web but haven't seen anything that may address my symptoms.

My truck did the same thing and still does to a degree. For what it's worth my 09 2500HD which for all intents was the identical truck did the same thing. It's not just your truck nor is it abnormal... it's likely all of them.

GM's tuning sucks for one... they can't figure out the most basic things like a working shift strategy. So what did I do with my 17? Custom tuning helped a bit but not a hell of a lot... it still will do the hang shift and just sit there revving with no load for no reason at all. Gears actually helped with it a lot... and I sort of counter the downshifting myself. With the 4.56's now I will downshift the truck to a sweet spot like around 3200 to 3500 ( fourth gear) at the base of the hill loaded and it holds it just fine. The odd thing is when I do that and then click up a gear at the top it actually upshifts and drops the rpm. If I let the truck do it's thing whether in tow haul or normal mode it does that rpm hang in a low gear it no longer needs to be in for what seems eternity before upshifting. I haven't found a tune work around for that.. and the way these E78 ecm's are I don't expect to either.

I know it's not right but considering I have experienced the exact same thing with more than one I don't think I will fix it without a better rewrite on the software.

Edited June 4, 2019 by SierraHD17

Jak860 · June 4, 2019

Thanks for the reply. At least I won't start chasing ghosts. I have 4.11 gears and live at 3000-7000 feet. I will be doing a supercharger as soon as I can drum up the extra cash. Hopefully it will keep me from having to drop down to a gear that screams.