I tried to recreate this using the brakes and could not get my tractor "jammed" in one speed. I tried the following different things:
Tractor in gear at speed, push in clutch, come to stop holding brake down, try to shift hi/low = success.
Tractor in gear at speed, push in clutch, shift out of gear, release clutch, come to stop holding brake down, try to shift hi/low = success.
Tractor in reverse, push in clutch, come to stop holding brake down, try to shift hi/low = success.
Ran out of ideas on combinations. Now I guess I will try the other brake since I was always using just one side (pedal closest to the transmission)
I did notice that at some times the hi/lo shift immediately would shift, other times you had to try/release pressure on lever and then try again (harder??) and it would shift. In other words is was not always smooth but it never acted like it didn't want to shift, sometimes it was a bit harder.
Sorry I couldn't replicate if for you, but glad for me I couldn't jam it.
