A buddy of mine is having problems with the motor in his '97 tahoe. If he tries to accelerate fast the motor backfires and wants to die. The only way he can get up to 50mph is by accelerating very slow, 50 is about the top speed. After about 2500 rpm's it does this. It also idles low, around 500-600rpms. Things that have been replaced are the egr valve, plugs, fuel filter, cats. I was thinking maybe the throttle position sensor? Anyone have some ideas?

fuel pump

check dist. and timing. make sure the plugs arnt fouled also

Buddy up to someone with a quality scan tool, not just a code reader.
Vortec's have been know to have intake gasket problems, and sometimes the injector/poppets in the intake.

600 rpm is about right idle speed.

Check the fuel filter as well I had that problem on auto theft deal great truck
Dumbass dealers didn't know. It was just clogged

If it backfires through the intake its too lean, probably lack of fuel pressure, I beleive it needs 55psi, not just at idle but at full throttle too,

I said the fuel pump because it sounds like one time with my 99 I filled the tank up without shutting the truck off, summer in AZ and i didn't want the ac to stop. the tank was sucking fumes low, and the fuel pump sits in the tank and uses the fuel to cool the pump. since I didn't shut the truck off the pump was more than likely out of the fuel and real warm. I dumped in cold gas and cracked the housing. I spend hundreds at three mechanics to diagnose what I thought the problem was all along. the truck would idle ok, and if I kept the rmp under 2500 it was fine, but if i tried to accelerate the pressure in the pump would blow the gas out the crack in the housing instead of down the fuel line. before dropping your tank remove your fuel filter and install an inline fuel filter, if that solves your problems then you know its the fuel pump in the tank

micky