i have a 2003 2500hd with 105k miles. at 95k miles i installed a 7-9in cognito lift with 37in toyos. for about 15k miles ive had a quadzilla set to 135hp. when i get on it from a stop it takes off fine until it gets into third gear then i seems to just rev up and not really pull but if i let off alittle it seems to pull harder. is my tranny slipping? it only does this in third gear and it never goes into limp mode. whats wrong? thanks

I'm sure that someone that knows more than I do will chime in, but I would think it your tranny was slipping it would do it in 5th gear long before it would in 3rd. Mabe a solinoid or something?

My truck does the same thing but in forth and fifth and I also use the Quadzilla2

Sounds like your going through the converter. Mine used to do that stock too. You're asking a lot of the ally with those 37s and a Quad 135. I've limped a few trans with that tune on stock tires.