i have a 99 truck and i put in a 02 high output motor. the tranny is still a 99 and the truck will not shift into overdrive. the tranny worked great intel i put in the new motor. the truck will go in overdrive if i haul a heavy load?? but empty no overdrive.

 

Is the output speed sensor plugged in or damaged on the tranny? My 99 would not go into OD and that was bad. $35 part, 2 minutes labor.

 

which ecm are you using? the ecm that came with the ho engine wouldn't have the programming for an automatic trans .
maybe i'm up in the night on this, but check it out
i looked in my manual and
i guess i'm up in the night the pcm controls the trans

 

The sensor (gov pres transducer) are different and non interchangable. Just got a beating over this problem. The Lockup, OD sol, and gov pres sol are the same but transducer for pressure and temp are not. Assuming your 2002 had an auto. you need the wiring harness and transducer for inside trans.