The Fleece Performance TapShifter allows you to shift your 2001-2005 GM Allison Transmission with the touch of a button just like the 2006 and newer trucks. Perfect for towing, drag racing, daily driving and everything in-between, the TapShifter installs in no time and provides factory-like operation, functionality and styling. The TapShifter can be used in the gas or diesel 2001-2005 trucks with an Allison Transmission. Installation: The TapShifter installs using OEM high quality connectors for a completely plug and play installation in less than 30 minutes. Operation: TapShifter Operation is very straight forward. To downshift depress the "-" button on the shifter. To upshift press the "+" button. The TapShifter will allow you to select a range with the shift lever and then tap up and down without worry of tapping to a higher range than selected. This feature is great for sled pullers who do not want to shift to 4th gear on the track! Features: Easy Plug and Play Installation Limits Up-Shifts Overdrive Disable Command Downshifts Decrease Gear Hunting Note: 01-02 models will require TCM Re-Flash to enable overdrive lock-out and proper function.