trouble code 51 on 92 astro van

Just bought a 92 Chevy Astro van ran fine on the test drive. On my way home it had a loss of power and when I stepped on it nothing for a few seconds then it rapped out like it was in neutral. Letting off the throttle I could feel the transmission shift then it was fine for about five miles and did it again. I hooked it up to a scan tool and it read trouble code 51 which is a faulty prom or ECM. I was wondering if anyone has had the similar problem and what the fix is or could possibly be.