I am going to replace my ecm in my car see if it can cure some on going issues I am having. I was thinking of going new from rock auto. Has anyone ordered a new ecm and prom from them does the PROM come pre programed to factory specs or do I have to write it myself. Also when replacing my ECM is there anything else I need other than the PROM I have a 1991 Formula 5.0 TBI stock other than an invisble cat. Thanks help would be appreciated.