I have a 98 geo  Tracker with an Auto tranny in it. the gas milage is around 18MPG and I know it dosent lock up and slips.  I have a 94 and 92 5 speed both complete and still in the trackers.  What problems will I have if I install the manuel? will it send a code to the check engine light?  Has anyone done this. It looks simple I have everything. Any advice. 
thanks

Jim