380sel starts and runs 2 minutes and gets worse then dies

Mercedes 380SEL 1982 145k miles 3.8L v8. Starts and runs great for about 1 minute, then gradually degrades and starts to sputter more and more until about the 2 minute mark when it starts to hesitate so bad that it eventually cuts out and dies. If I shut it off and start it again, the whole cycle repeats.

I have replaced the fuel pump, oxygen sensor, fuel relay switch, fuel reservoir, fuel distributor (which seemed to have improved the situation for awhile, but now it is back again after a few months) and half a dozen other parts that seemed to have no effect that I tried off of a salvaged wreck that I bought. It seems as though it is a fuel starvation problem, but I don't know. Maybe it is electrical or vacuum related? I can't figure it out. Any ideas would be much appreciated.

Thanks in advance,
Scott