I just received my package from TunerCat for tuning my OBDII L31 vortec.
Very nice package, includes everything needed (cables, interface black box etc) and the application is just as slick, if not more so, as the OBDI (LT1) program. It is significantly more money, but is a package deal, so I guess it isn't too bad!
Plus!!! the system is not VIN locked and my neighbors have several vehicles with the same drivetrain, so I can likely start recouping my costs a bit