Chevrolet Repair: ecm in a gmc r3500 w/ 5.7 tbi manual, oil pressure switch, engine oil pressure

Question
I have an 87 r3500 w/ 5.7 tbi and manual trans.
I have a friend that helped me narrow my problem to what should be the ecm.  I wanted to pick one up at the junkyard but I was wondering if other ecm's are interchangeable.  It seems that i've found that the part number for the ecm is supposed to be 1227747 but i noticed that in some listings the number is followed with some letters.  Can I use any ecm that has the numbers 1227747 as long as I use the old prom? And what are the chances that the prom could be bad?
thank you,
Sean
p.s. just so you know why we think this: The truck was running okay but the fuel would slowly cut off to the engine and every time i shut off and restarted the engine it would run ok again for another few minutes. It was also blowing ecmb fuses. We put a jumper on the relay to the fuel pump which my friend told me makes it bypass the relay and ecm. So with the jumper keeping the fuel pump running then the truck ran fine. That makes him think that it's the ecm because he says that relays are usually pretty full proof. Let me know your opinion.

Answer
I maintain a fleet of light trucks, and have not run across a bad prom yet, so I would bet any you get from a salvage yard should be good if it was running.
I might try replacing that relay though. They are pretty good, but a bad one could blow that fuse also.
There is also an oil pressure switch that should provide battery voltage to the fuel pump as long as there is 4PSI of engine oil pressure, so it must be disconnected or bad also, since it should bypass the relay also.