GM-GMC: fuel system, oil pressure switch, gm diesels

Question
i have a 1998 gmc sierra k 1500 5.7 i have replace the fuel filter fuel pump and relay i have gone threw 3 aftermarket fuel pumps 1 approx every 2 months someone said put a ac delco one in so i did new fuel pump works by testing it out of truck by power to pos and neg but no power in truck relay is kicking off and on like it suppose to but fuel pump isnt kicking on please help thank you vance

Answer
I do not have experience with newer gas engines, but I do know that the 6.5 GM diesels have a lot of trouble with the oil pressure switch (OPS) that runs an in-line eletrical fuel transfer pump.

I would suspect that the gas engine circuit is similar and I would try changing out the OPS to see if your problem goes away.