Had a 99 5.7 vortec with a hypertech handheld on it. Returned the handheld to stock and read the tune out and almost 1/2 the DTC's were showing X not reported including MAF, O2's MAP, IAT, etc. No way the truck would run with them deleted like they were but it would. I ended up just copying the DTC's from another known stock file and then tuned the truck. The fueling at WOT was WAY off for just having headers and it always showed OL. Is it possible the handheld corrupted something in the tune? Its a 99 OS 09360505 which I couldnt find a another tune with the OS.