A833 Four Speed Gets Stuck in Reverse

'66 Barracuda, A833 four speed, original New Process shifter. Car has recently on occasions got stuck in reverse, I get underneath the car and whack the shift lever to pop the reverse lever back into neutral so I can get it back into other gears.
Last night, I moved the car, put it into reverse several times. Each time it got stuck, five times in the dark I'm crawling under the car to whack it back into neutral.
Transmission was opened and inspected about 60 miles ago to check it out since I had bought this car, pronounced good and resealed. It really has not given me any problems until the last ten miles on it.
I did line up the shift levers a while ago and I plan to recheck it now. A few weeks ago, I shortened the reverse rod adjustment just a tiny bit thinking that might help.
Any other ideas welcomed. Thanks!