IDLE STAYS AT2500 AND WONT COME DOWN

there is a problem with the engine control system or a big air leak into the intake system. I'd guess that the check engine light is on. The check engine light indicates that the computer has detected a malfunction in the engine/emission control system and has diagnostic codes and data stored which would be essential in diagnosing the problem. A technician with a scanner could access the diagnostic codes and data and then be able to give you a diagnosis. If you want to find a GM specialist, here's our directory link for you: https://repairpal.com/gmc-repair-in-new-castle-pennsylvania