You could pull the transmission
http://www.grandprixforums.net/how-r...ion-35485.html

Then remove the side cover, valve body/channel plate as a combo, remove input shaft o-ring then you can lift up the chain/gears. and change the gears. The link below shows how to do most of this, and suggests the 4th hub (03 or below should consider doing this automatically)
http://www.grandprixforums.net/how-t...ess-54448.html

Then you need to program it. Here are the HPT instructions
http://www.grandprixforums.net/how-p...hpt-75323.html