I have hp tuner a friend has had two 5.3 trucks both would go to nuetral when letting off gas while in tow haul mode. Mine doesn't do that and the one he has now is an 04 like mine. Is there a way to stop his from doing it?

 

Try copying the normal shift table into the performance table. Maybe someone messed with it.

 

what it does is when you let off the gas it coasts freely with no hold back. then when you give it gas it revs up to get untill it catches.

 

How do you know it's going into neutral if you let off the gas?
Tow/Haul allows the Converter to stay unlocked longer so you can maintain more RPMS where more power is while pulling. When you let off the gas the converter unlocks and the rpms drop down more than when locked because it releases the load off of the engine.

Has his tune been messed with any that you know of?

Edit: You posted while I was typing. It's working as designed. It's not going into Neutral, it's just unlocking the converter

 

Is yours tuned but his isn't or vise versa?

 

his hasn't been messed with. I had a 99 that didn't do it, and my 04 didn't doesn't do it even before i started tuning on it. If he is going over a hill rpms will drop to idle and you can rev it up like its in neutral until it gets to whatever rpms it needs for the speed its going. His 03 done it and now his 04 does it. Both were gmc's though, where both of mine were chevy.

 

Sounds normal to me.
At what rpm does it start moving again with tow/haul on? Can you get a video clip of the tach?
Here's a video of mine without and then with tow haul on. the exception is that I have a Circle D stall converter.

http://s175.photobucket.com/albums/w...5-45th-nth.mp4

I doubt there's a stall difference between GMC and Chevy but I suppose it's possible.

 

What is actually happening is the overrun clutch or band is not working and or the TCC is staying engauged. ether way copying the normal tables to the performance will solve this, but you can use the VCM controls to manually lock and unlock the converter and lock the trans in each gear, but it sounds normal to me.