Here is a copy of the post I made for you on the other thread yesterday:
Bill, this is a 30 second fix on an open station, 5 minutes on a cab. It is just an external linkage issue. Your 4-speed shifter, like most Japanese and some Korean models, is made to shift in an H pattern. If you sort of go in an X pattern quickly, you can sometimes engage two gears. If you try to do it, you can't make it happen....but we get this call about twice a year and it is an easy fix. I've posted a solution before, but if you are like me you can't use the search function well enough to find old threads!
Under the seat, below your left cheek is a metal cover with 4 10mm (I think) bolt heads. It is sort of rectangular, and just inboard of the shifter. Take this off. Wiggle the 4-speed shifter a little and you can see how this works. You will see the sideways H shaped part of the mechanism and that you have got this in a jam. The H engages one or the other of the shift levers. When you pull it to the left, it does 1st or 2nd. When you pull it towards your hip and then fore or aft, it does 3rd and 4th. You can see how that works. Now take a Crescent wrench or pliers and put these levers back into position and all is well. Spray a little WD40 on it while you are there.
Let us know that this worked.