Looking for some advice on a Christmas gift for my father. He's always takes about picking up one of those tuners for his 05 duramax pickup. It's one of those gifts he'd never get himself but always wanted. Any input on the handheld tuners? Or is there any decent tuners in the Chicagoland area that mess with Chevy diesels? He would just be mainly looking for increased power, mpg, and drivability.