I don't have any hands on experience with second gen, but the sequence of events you wrote isn't making any sense to me. You said the original problem was a CEL, but the "car ran fine". Now, after all of the repairs at the shop, it "runs like a pig". If both of those statements are true, then something with the repairs must have caused the current performance problem (and not a preexisting condition). First thing that comes to mind is not setting the timing correctly when the belt was replaced.