i have a 2001 gmc savana 3/4 ton 5.7 vortec, i am having problems with a rough/low idle and it dies under load and has no power. i have replaced the fuel pump, fuel filter, spark plugs wires, plugs, rotor, cap, air filter, MAF sensor, TPS sensor, idle air control sensor, EGR valve. i am out ideas please help. By the way i have NO codes.

Sounds like could be low compression on cylinder,remove each plug one at a time and test with a compression checker,if you dont have one you can rent one a your local parts store.Remove fuel pump relay to keep engine from cranking and test each cylinder ,They should be at least 45 to 50 pounds and hold it.have someone to turn car over while you test the pressure in each plug hole. Remeber it must hold the pressure.if you find one that is low pressure you may have to have head work done. It sounds like you have done every thing else you can do.Best of luck to you,,