My truck is stuck in fifth (I assume) gear. Seems like it somehow went in gear as I was trying to get it into reverse. . I have to open the top I assume. . What do I look for that is probably excessively worn. . Are the worn parts on the top removeable case or am I looking at transmission removal with an overhaul?? It has been a little difficult to get into rev-often I'd go up to fifth-then down. Somebody explain what's going on with this thing?