I put my 383 back in my 95z and it started and ran strong for a good 15 minutes. Then out of the blue the car just stalled. It restarts strong but only runs for about 3 to 5 seconds then dies out. Theses no security light on when this happens, but is it still possible that the VATS is causing the problem?

 

Check the fuel pressure. A dead giveaway of a dying fuel pump is one that works for a few minutes, shuts down, then after resting for a bit, starts up again.