I have a 1999 gmc sierra 1500 4.3l. It start good, after about 20 seconds it starts running rough erratic idle and no throttle response. I've had ongoing problems with this truck for about a year now. I have replaced the distributor twice ignition coil fuel injectors (spider) and crankshaft sensor. I also drained and replenished fuel, all to no avail. No trouble codes present.

How about fuel pressure? It should be at least 60 psi. at the line going into the TBI.

I agree sounds like the fuel pump may be on its last legs.

Gonna check fuel pressure again. Thanks! I'll let you know.

Fuel pressure 58 to 62 psi even when engine starts running rough and wants to die fuel press actually goes up to about 62 to63.

OK, fuel pressure sounds good, yes regulate the tbi pressure to 18 lbs. The back fire is normally in the timing but I believe you can not adjust it on your motor. How many miles on the truck?

Another thing to look at are the sensors. One sensor that causes grief is the temperature sensor, either at the thermostat housing or on the side of usually the left side head. I believe your problem is with fuel delivery and there sensors that can cause it. How dose the truck drive down the road at 55, or what ever speed above this you like to drive...