1) Isn't the kickdown switch a toggle? just snap it once and see if that clears it up. but it should try to be in the lowest gear possible for the speed if that is the case. Or just disconnect it right there under the throttle and see what happens. Or, get up to the 3rd gear red line and see if it shifts up.

2) there are small plastic/nylon/whatever bushing in the shifter linkage that could keep from being in the indicated gear. I just replaces some and it took all the slop and confusion out of gear selection. Based on this one data point they seem to last ~30 years

3) you can test for ^ by trying to ease the shifter ahead toward N just a bit and see if completes the shift.