I also have a 2004 silverado 5.3 64,000 miles with 20' rims and tires. i am having some of the same problems as another member. Sometimes when i mash the gas the truck takes off...not as much as it used to but it goes....then some times i feel i could walk faster than the damn thing its almost embarrassing...can anyone help?

 

one of my buddies told me possible fuel pump...or fuel filter??? i want my power back!!!!

 

He could be right. Replace the fuel filter first since that's the easiest and cheapest to do.
It could be partially clogged. Good luck.

 

If that does't help,perform engine tune-up and check exhaust back pressure test as well.

 

Other things to check isthevolume and pressure from the fuel pump/Fuel pressure regulator/Injectors/even a gas cap can give you problems.

 

My 2007 seems to do the same thing. Only 24,000 miles on it. Going to have the dealer check it when I have them do some other work.

 

I am not usre if that model has EGR valve, but they can bind and then work . If its open power goes west.

 

maybe clogged injectors also