My X Type with 110K miles would shift up through all gears when starting out from a stop, but when brakeing and slowing down it would downshift through the gears , but at the point where it should have been in 3rd gear it would be in neutral. I changed the ATF fluid using the Castrol Special Import and then made sure oil level was proper and still had the problem.
Rotating the elctrical switch on top of the transmission (J gate adjustment?) slightly one way made things worse. When rotating the switch in the opposite dirrection it seemed to drop into a natural detent and the problem was fixed. I now have over 1000 miles on the car since the repair and have not had any problems. You have to remove the battery and battery box to get at this switch. It is directly on top of the transmission and is bolted down with 2 bolts. there is a slot under one of the bolts and when loostened the switch will rotate left and right. I hope this helps someone.

 

Thanks for this topic, good to see it worked for you

 

railroader, thanks for the tidbit of information. That is a problem that is fairly unique and I can't say that I have seen it around the forums all that much.

On a side note, which railroad do you model, UP here.