Hupp Transmission Stuck in Two Gears

My Hupp Transmission got stuck in low gear on my TO-20. It only works in the neutral position on the Hupp. If you shift it up or down it stalls the motor. When you let the clutch out, it feels like it is in low. All gears work fine on the transmission. Any suggestions?

You have probably got your overdrive transmission stuck in two gears. This can happen and it may be necessary to split the tractor and disassemble the transmission to fix the problem. I am including a link to a guy that is pretty much the guru of tractor overdrive transmissions.
http://www.oldfordtractors.com/sherman.htm
Hupp had a problem with early models tendency to do this and a upgrade kit was made available to cure this problem. Since Hupp is no longer in business these kits are no longer available