Another easy way to tell, is the control unit is under the hood and mounted to the firewall just above the brake booster. I had to flush my trans. at approx. 26000 miles because I was getting the rumble thru drivetrain on freeway. I used mercedes fluid that is for fuel efficient trans. It had been about 3000 miles with no issues. Truck was also already tuned at 21000 miles by Pat G. Tuned makes truck night and day better.