my old truck has a mind of its own. was going down the road and the t-case switch in to neutral or just between gears. I put it back in 2wd and started again. then it switch into low range later. the shifter didnt move. now it is in 4 lo. shifter is in 2wd. what is going on? is this a common problem? easy fix or replace it? its a a 89 f150