The 4L75e is not a production transmission and was only available through a GM parts distributor If your original transmission has an internal input speed sensor, 4L65e, 4L70e, 4L75e (beginning in 2006 and later), the WATRA31-18 is required. Check your ECU in the red (or green connector) for a Red-Black Stripe wire at pin 22, and a blue-white stripe wire at pin 23**or** In the TCM, Red-Black Stripe at pin 3, and Blue-White Stripe at pin 45. If these wires are not there, then you do not have an internal input speed sensor, so you would need the WATRA30-18 Check your RPO codes in your glove box for RPO M30 (4L60e) or M32 (4L65e). This may or may not guarantee that you don't have an internal speed sensor. Count the pins on your original harness transmission connector: If you have 11 pins, you will need the WATRA30-18; If you have 13 or more pins, then you will need the WATRA31-18