shifting hard

[kfdfire3]

New to site....I have 2008 gmc 4×4 3500 HD dually*
The efi was installed by a (professional) however they can not figure out why when tune is in tow and I have tow/haul selected on my shifter why does it slam into third gear. I have had them repeatedly try to fix this and and still nothing. Any help and or suggestions would be great*
Thanks

 

[Matt750]

In tow/haul your torque converter is locked out, don't know if tow/haul mode boosts line pressure, but it does carry each gear a little longer before the up shift as well, in your tow tune there may be some changes in the TCM programming. If your tow tune is telling your transmission to shift differently than the stock tune, tow/haul mode could be magnifying the discrepancy. Also check your tire size, if they are larger/smaller than stock there are adjustments to be made in both ecm and tcm values. These points would be a few things to consider relative to your problem. If all the numbers are correct, you can try doing a TAPS reset. Hope something here helps.

 

[03spoolindmax]

In tow/haul your torque converter is locked out, don't know if tow/haul mode boosts line pressure, but it does carry each gear a little longer before the up shift as well, in your tow tune there may be some changes in the TCM programming. If your tow tune is telling your transmission to shift differently than the stock tune, tow/haul mode could be magnifying the discrepancy. Also check your tire size, if they are larger/smaller than stock there are adjustments to be made in both ecm and tcm values. These points would be a few things to consider relative to your problem. If all the numbers are correct, you can try doing a TAPS reset. Hope something here helps.

Not sure what you're talking about. In tow haul the converter is locked halfway threw 2nd gear and up. With a stock trans either in tow haul or not. When the converter locks. The line pressure drops around 90 psi or so. If he just got EFI live done I doubt anything was touched in the TCM programming unless he also got a seperate TCM tune.

To the OP, if this problem wasn't there before the tunes there's a chance it could be the tuning. But it doesn't hurt to change the spin on filter and do a TAPS reset with a V2 or allison DOC software. Then go from there.

 

[Matt750]

I was just spit ballinga few ideas since it sounds as though he didn't know what his guy had changed when tuning the truck.