[tsubaki]

Besides, you probably need to service those reels, all the fish ya'll been catching.
Barring replacement of parts in the foot or improper installation, is it possible:
The shift rod may be slightly out of time with the linkage and not be able to be adjusted out with the cables? I think that model unscrews.
Where the shift cable clamps at the motor (adjustment location) is it tight in the holder or sloppy?
The control box is worn, say the pin or bushing for the forward and reverse?
The cable length is incorrect in the control box?
Just stuff to think about.
I did find on one occasion the setscrews for the cable at the end where you may cut it off, on one side the setscrew was all the way out and on the other side the other screw was tightened into the cable enough to bend it and hold for a while.
The end result was irregular position of the shifter at any given time. Convinced the cable was simply worn and removing it, I found the problem.
The cable could move about 1/4" beyond the intended adjustment, thus creating the same problem you have.
I thought I would never get it pulled out to straighten it.
Doubt you will find the same thing.

By the way do you have the parts list for your winch?
I can't locate mine and need the spring brake and a place to order it from.