First off, it would help everyone on the forum if we knew what kind of truck we were talking about here. But yes, pcm and ecm are one in the same....(if history serves me right).

ECM (Electronic Control Module)is what the main computer was called before 1996 (I believe).

PCM (Power-train Control Module)is what those same computers are called now after government regulated a whole bunch of terminology with regards to computers and OBD ll codes (trouble codes)mostly from 1996 and later.

But here's the thing about your situation. You say the Isuzu tech said that your PCM is overheating? I would want to know why it's overheating before I went out and replaced it. I have an '89 with the original ECM and (knock on wood) even after all these years, it still works fine. These computers are not usually delicate or prone to overheating. I mean, who's to say if you replace it that the new one wouldn't just overheat as well. Without knowing the source of the problem, it could happen. I would definitely get a second opinion.

Personally, if you have a college near-by with an Automotive curriculum, I would go and ask one of the instructors for advice on this. Most instructors are there because they have years (20 to 30 in most cases) of experience and a good deal either own or have owned a service garage. Automotive curriculums usually have an "Automotive Electronics Instructor" who would probably be the best for the advice you are seeking. Once again, that is my personal opinion but it has worked for me in the past....many times.

Hope this helps...good luck...

dawn...