I put a heater core in my jeep this weekend and now the tranny is not functioning properly. Reverse works great but when I put it in drive, it wants to start in over drive... Will not shift gears like it's supposed to. When I manually shift it works fine. I checked fuses and made sure the computer was plugged in. What could it be

 

Well neither heater core or tranny are related. You did something wrong either taking it out or putting it in. I'd start back tracking your steps

 

Sure they are. The TCU is unplugged under the glovebox..................

 

The tcu is plugged in... Still a no go. (Silver box, multiple pin plug?)

 

You get what in saying though right? Lol the heater core isn't going to effect the tranny, it's the steps he took to get out the heater core or putting it back in that is going to possibly disconnect a wire or something

 

Absolutely I get what you're saying.