Cruise control problem

I have an 03 5.3l ava. I have a problem that only happens when the cruise is on and engaged. When it tries to hard accelerate, like going up a hill, it feels like it pops out of gear. It will accelerate wildly and it stops pulling. All I have to do is tap the brakes, to release the cruise, or turn the cruise off and everything goes back to normal. It only happens with the cruise on and engaged. Never with it just on and not engaged or off completely. How don't fix? Where don't look?

this sounds like your trans may be slipping. next time you are driving and find a place that this would happen, disengage cruise control and just use the peddle. try to make the truck go from steady speed in overdrive to a third gear kick down, IE 4-3 shift. does it free rev? if no then give it more throttle and try to make it go from overdrive to second, IE punch it 4-2 shift. does it free rev here? if the answer is yes to either of these then baby the truck as much as possible until you can get to a trans shop/mechanic. also more helpful info would be how long have you owned it? IE new to you or a few years or since new. did this problem just start or has it done it the whole time you have owned it? has it gotten worse slowly or was it sudden? any mods to the truck? IE big tires, re-gear, things that added a lot of weight. if your problem is literally only when cruise control is active then there is a lot more to your problem.

Thanks for the info. In both cases it drives like normal. When cruise is off, or even not engaged, it drives normal (drops down a gear or two and accelerates like it should. I think that if it was the transmission it would happen all the time or when the cruise is off. Problem only occurs when cruise is engaged. I have owned this vehicle for 18 months. I think I'm 3rd owner. I have larger than factory tires on but not monster tires and rims. Problem started about a year ago and has come and gone. Sometimes worse than other times.