I recently purchased a 2001 Trooper limited with 117,000 miles. Looks and runs perfect. I bought it because the previous owner spent $2400 for new rebuilt transmission. It worked for a month and now ONLY reverse works. The previous owner was refunded her money since the mechanic couldn't figure it out. ? I looked through the glove box and found a receipt​ for a rebuilt transmission dated in 2013. So what could be the Problem with this transmission?? It's 99.9% new! HELP ME!!

 

This is a bit of a long shot, but maybe the transmission range/mode switch.
It's mounted in the side of the trans where the shift lever mounts.
It tells the trans ECM what gear the trans is in (or should be in).
They go bad and send false info to the ECM.

Otherwise it could be a big trans problem.

 

Thank you so much for your opinion as I need as many as I can Get.