Dw5574

I have a 1989 Camaro IROC-Z with the 5.7l TPI. I originally had it scanned and it was codes 41 and 42. I popped the Prom out and put it back in and it ran for for about a day and check engine light came back on but this time only code 41. car doesnt want to idle right, runs rich, and doesnt feel like it has no power. i checked the ground for code 41 (which is cylinder select error) just trying to figure out what it could possibly be. It has a hypertech Prom in the car. Does anyone know what i should check or replace?