I just recently changed my 98 GT from a supercharged setup back to stock. Car runs fine, idles fine, drives fine, but after half pedal it loses power. Recently changed spark plugs and wires, IAC, and the module that controls the EGR valve. No vacuum leaks. Cats not glowing. Pulled the Diablo chip out of the computer. Car still has Walboro 255. Other than falling on its face from half pedal on, the car runs great. When I try to run past half pedal, exhaust has a weird smell and code scanner keeps saying right and left banks running lean.

Is the tune still in the stock computer? What else could cause this?