Hi I have a 94 c1500 that I just swapped over to a 350TBI from a 4.3TBI. I used 350 knock sensors. throttle body, injectors, full distributor(with ICM and ETC) and PROM chip. When I put the PROM chip in it the ECM retards the timing rediculously. I put the 4.3 PROM chip back in it and it runs 10 times better. I mean of course it doesnt have the power or that a 350 should and it surges a little due to the fact that its all running on the 4.3 chip, but even so it still runs tons more power than when I run the 350 chip. I don't know what else to do. Any ideas whats causing it to retard the timing so bad when I put the 350 PROM in?