With out knowing how it is acting, I would suggest you try this to eliminate a weird cause.
With it sitting for an hour, in a cleared location; crank. let warm up, idle. Do not have touched any direction control.
Then move direction control to forward, accelerate a little. See if it moves at that engine speed.. If it does, accelerate some more. Then move direction control to neutral, pause, then to reverse....
This to see if whatever pressure release on trans is cause.
Examine any linkage from any foot control; to pause, to see it is free and allows full movement for each direction desired. They get corroded, bent, jammed with debris you have traveled over...
The typical warehouse forklift had a way to disengage the trans while lifting the forks. Many transmissions have been rebuilt and only improve because in the removal and disassembly this connection/linkage, was freed up and now functions.
Just from pics, it appears the Ford box is a ground speed range. Is the front box by any chance a Funks
power shift?