The transmission does not have that many miles on it since it was overhauled and ran good. It does sit a lot and now it will go into reverse but putting it in any forward gear, it does not go.
Car? mileage? engine?
But it does sound like the transmission.
Check your linkage to make sure it is functioning properly. If that looks ok, I would guess something stuck in the valve body. you should be able to make repairs without removing the tranny.
A pressure guage would be of some help. Line pressure/line rise check in forward gears.
If it sits a lot, it’s possible some internal seals are drying out and leaking pressure. (especially if it was a cheap rebuild) I had a Chrysler tranny that would do this and not go INTO reverse until it warmed up. Does it improve if you let the car completely warm up? Have you checked the fluid level?