The only way to know what tune is in the truck is to attempt to read it out. I say attempt because when custom tuners make tunes, they usually lock them so they can't be viewed or modified. In other words, you may be able to read the tune out, but not be able to view the actual calibration values. Also, we don't even know what brand of tuning tool was used. HP tuners is most likely, but Efilive and a whole host of canned tuners work on these trucks as well. I would recommend having someone with an HP tuners tool try reading the truck. If you're lucky, and the tune is not locked, you will be able to keep your tune, but modify the emmission parameters (readiness monitors and DTCs) back to stock. Your other options are simply flashing back to stock, or getting a new performance tune that is emmissions compliant.

James Kuhns
Owner/Technician
Auto Tech Solutions
Chatham, New York, USA