Want to accelerate only when the belt squeaks.

Why would my truck start up fine but then act as if it wants to stall out and not want to accelerate only when the belt squeaks. My truck starts up just fine normally but sometimes the belt starts to squeak and we have already replaced the belt it stops after awhile as long as I turn off the heat! Now its getting worse but its starting to put and wanting to stall when it starts squeaking and the lights seem to go dim as well. We have already had the trasmission rebuilt in the truck as well.

I am woundering what could cause the truck to be fine and then want to stall in the middle of driving it as well as putting and not wanting to accelerate then it will after the belt stops making the noise. I dont know if it is the battery maybe causing this if it is starting to drain out or what it could be do you think you might know o and its an automatic chevy silverado 96 2 wheel drive