1995 GMC Truck engine will idle, but not rev up

I recently put an 89 small block 350 into my 95 gmc truck. Everything bolted up easily, including all wiring and fuel lines. My problem is that the motor will idle at 1000 rpms all day long, without any hesitation. The very second I try and run the throttle, either from inside the cab or the side of the tbi, it bogs out and stalls, if I floorboard it, it does the same only backfires out thru the tbi. I have checked my map sensor as well as tp sensor, all are at correct voltages. I had a spare fuel pump in which I changed out to see a difference also. The pump was brand new. Am I not getting enough fuel pressure and thats the reason for the backfire or is there something else I should be looking for? Also could the plug wires be a problem?