[quot]The engine runs excellent but the check engine light stays on constantly.
If I jumper the ALDL plug to flash for codes the light does not flash, it just stays lit the entire time. [/quote]

This is a problem. You should see code 12 with the key on, engine off, and ALDL jumpered. Doesn't matter what other codes are present.

Start with the "ecm self test" function. Turn the key off for five minutes. Then turn the key on but do not start the vehicle. The check engine light should light for a few seconds, turn off for a few seconds, then light and remain lit. If this function is not happening you need to: 1) confirm the wiring for the check engine lamp is correct, and 2) confirm the prom is not corrupt or installed incorrectly. Confirming the prom is a matter of removing it and installing a known good prom, then going through the steps
for the self test again.