I've noticed that my FLU419 is getting harder and harder to shift into 1st and 3rd gear. It doesn't seem to go completely into those two gears....it will pop out if I don't hold the gear shift. Is there a shift fork or some sort of linkage that can cause this? I drive the thing quite frequently and it has just started doing this the last few times. When in gear it drives fine.....its just tough to get it into the 2 positions towards the front of the cab (1st and 3rd gear). Any suggestions? I haven't taken anything apart to look. Thanks.