My explorer is stuck in low gear. its running third gear at 25 miles and hour and lil over 3,000 rpms. it wont shift into four. had it back from a tranny shop for about a month and this problem occurred. took it back down there, they replaced the torque converter and looked at the tranny and put it back in and still have the same problem. my guess is the transfer case but, before i pull it back out again for the third time in a lil over a year i wanted to get some other advice or insight. any help greatly appreciated