If you want to disable V8 & V6 cylinder deactivation without reflashing computer modules, this OBDII port "Plug & Play" device is about as simple and good as you can get. Made in the USA. I have had no issues with the device working or draining battery left unattended.*
A friendly caution: Unplugging this device can (or has) reset emission readiness status. Thus, if you are due for emission inspection, it is recommended to remove the device and let the vehicle re-establish emission readiness. If the vehicle is driven daily, a week prior should be enough. A little research on the vehicle could lend specific driving patterns / cycles to establish readiness in as little as a day, however it is desirable to have an OBDII emissions reader to know readiness status for guidance.
*Range Technology States "It is suggested the device be unplugged if the vehicle is not being driven daily or left for a few days. There may be a power draw on the battery in some applications."
If unsure, please check with Range Technology for compatibility with your vehicle.