The ATS Co-Pilot transmission controller is recommended for use with light duty pickup trucks with a heavy-duty aftermarket transmission and torque converter package installed. While the Co-Pilot will still function perfectly on a stock transmission, factory transmission shafts are weak and prone to breakage. The factory torque converter clutch will also fail if applied under high load conditions. Factory computers are programmed to disengage lockup under certain conditions which will protect the transmissions internal components under higher load. This is when we recommend having a heavy-duty aftermarket transmission installed on your vehicle to prevent transmission failure. If you have a stock transmission it is recommended that you leave your Co-Pilot in a less aggressive setting when under high load conditions.