95 GMC with 5.3 Chevy=== won't shift?????
 

Installed 5.3 into 95 GMC truck. Took for a spin, and it won't shift into 3rd , 4th, and so on. It has a 4l60e transmission from the 95 truck. The harness is a S& P emmissions legal harness. The speedometer won't work either. Tried piggybacking the old VSS wires to the new, still nothing. Also, sometimes the truck won't start right away. S & P mentioned to run their fuel pump relay, but why? The 95 has its own relay, why use theirs? Anybody??