Jeep Grand Cherokee Stalling

I have a 1997 Grand Cherokee 4 L that has been having problems stalling; seems electrical to me; complete loss of power. Sometimes power would restore and sometimes it would give me a hard time restarting. Occasionally when power did restore the engine would backfire (you could smell the buildup of fuel). I replaced the spark plugs, spark plug wires, distributor cap and rotor. The problem remained. I took it to the dealer to have it checked, they stated that the ignition coil has an open circuit, the MAP sensor has too high a voltage and the PCM has an internal failure. I proceeded to resolve the issue myself by order of cost.

I replaced the ignition coil; the engine still cut out although it seemed not as frequently and it occasionally backfired. I replaced the MAP sensor (dealer part); the engine seems like it runs smoother, my gas mileage definitely improved; the engine still cuts out and it occasionally backfires. The last time the engine backfired it blew my muffler (so much for the cheaper muffler, when I get this resolved Im spending the extra money on a muffler).

The dealer wants $670 for the PCM and I am not ready to pay this. Ill try backing out the screws and see what happens. Also, should I have had the PCM reprogrammed after replacing the MAP sensor? What do you think?

Thanks in advance for any help.