2001-2002 trucks unfortunately are not equipped with this ability to hold 4th gear ('lock-out' overdrive), thus making towing in hilly conditions a bit of a chore. Due to numerous customer complaints, GM released an updated TCM (transmission control module) software calibration that added this "overdrive lockout" feature, so owners of 2001-2002 trucks could select 4th gear at the push of a button. However, this required an unsightly and clumsy aftermarket push-button switch to be mounted on the dash.
Selecting 4th gear (or 'locking out' overdrive) on the 2003-2005 GM pickup trucks with the Allison transmission is accomplished simply by holding the tow/haul button for a few moments. This was the elegant and more streamlined solution for selecting 4th gear, as opposed to having a separate button in the 2001-2002 applications.
BT DieselWorks has now developed a solution for the 2001-2002 truck owners who wish to have overdrive-lockout functionality, while maintaining a clean, factory appearance. What this kit does is retrofit the tow/haul-button-activated overdrive lockout functionality of the 2003-2005 trucks to the 2001-2002 trucks. With this kit installed on your 2001-2002 truck, overdrive lockout is accomplished the same way as the 2003-2005 trucks. Press the tow/haul button briefly to turn tow/haul mode on/off, and hold the tow/haul button for ~1/2 second to turn overdrive lockout on/off.
Everything required to install the module is included in the kit. Factory Delphi connectors and pins are included with this kit so there is no cutting/splicing of the factory shifter cable.
NOTE: This is also a great product for the 2003-2005 truck owners who run 2001-2002 TCM software. Many people prefer the 2001-2002 TCM software due to its cleaner shifting under high horsepower. If you run a 2001-2002 TCM in your 2003-2005 truck, you lose the tow/haul button overdrive lockout feature. With a 2001-2002 TCM installed in a 2003-2005 truck, the overdrive lockout light on the dash will still illuminate, but the transmission will not actually downshift to 4th gear. With this kit installed in a 2003-2005 truck, you can regain that factory-style overdrive lockout function while running a 2001-2002 TCM!
IMPORTANT NOTE: If you have a 2001 or early 2002 truck, you may or may not need a TCM software update to enable overdrive lockout capability and allow this overdrive lockout kit to work properly. Your dealer can reflash your TCM with the latest software to enable the overdrive lockout feature. If your dealer is far away or uncooperative, I can provide you with a pre-flashed TCM on a core-exchange routine for $50 (generally dealers will charge 1 hours' to relfash, which can be upwards of $100) plus shipping.