I am having trouble with 1990 chev 2500 Muncie 4 speed (m20??) not easily shifting into 3rd & 4th and reverse. It seems you have to wiggle the shifter into the shift gate and wiggle it into reverse. The problem happened all of a sudden so its not regular ware. It is a snow plow so we need reverse quite a bit. With the shift stick out you can site down and see the shift gates and they look lined up OK. Need help. Any ideas????