64 Dodge Dart 904 transmission issues
 

Ok sounds have a 64 dart 225 slant six with i believe a 904 transmission. Motor has been rebuilt and is running great. We drive it about one a month between 1-2 hour drives. I moved the other day and drove it to our new house 1.5 hr away mostly 55mph. No issues there. The next weekend i noticed it was have trouble getting into gear. I let it warm up a little longer and didn’t have anymore issues. So the next time i took it out the only way to get it into any gear was high revs, 3-4K. Drove it around town and somehow made it into my garage by high reving it into gear. Now nothing! Can’t get any gear at all. Things i have checked:

Throttling cable- no issues
Push button gear selector- no issues up top or on tans
Drained and removed filter and replaced- no big metal chunks. Just usual soot. But clean
Put everything back and filled and turned car on, warmed up and had to add more fluid to get to level while warm which i assume means pump is working.

Please help! I don’t have much knowledge on transmission like i have on engine as we always stayed away from them

Checklist 1. Did the transmission fluid smell either like burnt oil or varnish when you drained it?
2. The big one! Is the transmission reading full IN NEUTRAL while idling warm?
3. If the above is negative, it all is pointing to a weak front pump. You could put a pressure gauge on the transmission and read the pressures. A local Transmission shop could give you a full reading. Pump is located behind the torque converter.
Remove tranny, remove torque converter, you'll need two slide hammers to remove the pump that's sits
in the opening of the transmission.