Ok I have a 1996 explorer I was driving at 70 mph. all of a sudden my tach went up and was like I was in Neutral. had to get towed.. So I pulled the shift motor off and turned the case by hand into gears. well I put the shift motor back on 2 wheel worked again.went 6 miles and it did it again, went into like neutral, well I shift it to 4 wheel low and it works, But now I push the 4 wheel button to go back into 2 wheel and wont work , neither 4 hi, but works in 4 low. when I had shift motor off I had my brother push button to make it move and it did that. Im wondering if the case is bad or the shift motor not holding tension or moving in the right spot?