I have a 2003 Chevy TB 4WD with 155,560 miles that has given me very little trouble. I replaced the alternator 4 days ago and yesterday after I got off the interstate, it began surging. I had a diagnostic done on it this morning saying that the MAP (module air pressure) sensor was bad. I bought and replaced it, but the problem remained. I had the code cleared and drove it approximately 50 miles hoping that the pc would cycle and correct the issue. This did not happen and the RPM's continue to rev and drop, even to the point of it shutting off at red lights, stop signs and during low speed braking. When driving on the interstate today, I engaged the cruise control. It maintained a steady 2100 RPM, but i could feel a control module closing and opening. I need to know if this sounds more like the TPS (throttle position sensor), the MAF (mass airflow sensor), or something else, like an Oxygen sensor?