Our tuning for the 2005-2009 Envoy 5.3l helps gain performance and better driveability. We include custom proprietary fuel and spark table changes that will make your truck more lively at part throttle and unleash great power differences. Our tuning on stock vehicles normally yields gains of 15-20hp+ and 1-2mpg increases as well – the more modifications you have the more you will benefit from the tune. After placing your order, please fill out an order sheet for your vehicle (here). What program should I use and what is refundable? Click here!