Recently, I experienced an engine failure with my 2001 GT. I replaced the engine with a 2004 GT engine, and since then I've been having problems. I had my battery and alternator replaced in the process after the engine failure because the alternator was bad and the battery needed to be changed. Since I've replaced the alternator, battery, and engine, the RPMs jump as if the computer is hunting, my battery light will randomly come on and disappear, my check engine light stays on and never goes away, even after fixing the problems and clearing the codes, and sometimes my car will experience a random short misfire and not run on all cylinders when driving, and then it will clear up. Do I need to replace my ECU/ECM? If so, do I need to get an ECU/ECM that matches the year of the engine or the VIN # on the car?