turbo 6.2 wont stay running

my twin brother and I just did an engine swap in a 92 chevy 6.2 diesel with another 6.2 that we put head studs and a GM1 turbo from a 92 6.5 diesel. couldn't get it to start till we put some oil down each cylinder and it got enough compression to start. due to this engine sitting for so long we think it had dry rings. at first, it was running just fine, would idle and rev as it should. took it for a little test drive and it died just down the road from our place. got it limped home and then it would just start for a second then die like the fuel shut off or the key was turned off. so we did the following... changed the lift pump, changed the fuel shut off solenoid on top of the IP. got it to start today who knows how.. so while it was running we were bleeding the injectors seemed to run a little better as we bled each injector and then out of the blue it quit just like previous and doing the same thing starts for a second and then shuts off. we tested fuel pressure and its 7-8psi while running. Not sure where to go from here. have fuel to every injector. I'm sure we are missing something stupid or hopefully, it's not the IP. forgot to add that the service engine soon light is on.

figured it out, changed the injection pump and it runs like a champ

Welcome aboard, and thank you for updating. Very well explained.

Did you identify the code causing the SES lamp? Or did it go away once it started and ran well? The SES lamp should come on at key ON, but go away when it starts. If it's still there, pull the code (paper clip method, no scanner required). If you get a repeating "1-2", it only means the diagnostic system is functioning normally, and there are no pending DTC's.