VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc transmission works intermittently

I have a 1946 Chevy 3600 ¾ ton truck that I am in the process of getting road worthy. I am a beginner mechanic, first time tackling an older vehicle. Got the engine running and just finished getting all the brake components take care of. Since it was up on jack stands I realized it would be a good time to run it through the gears. I replaced the transmission fluid since it was pretty dirty. The first time I tried it every gear including reverse spun the tires. The next few times I have tried to run through the gears it doesn't always spin the tires. One time, only third and fourth gear worked, another time only a couple of gears rotated very slowly, another time second, third, and fourth worked well, and reverse was slow even when revving the engine. Is it time to replace the clutch? Weird that it is not consistent.
Any thoughts would be greatly appreciated.

If it was mine I would wait until it was on the road and driven a little. It may be the clutch disc or pressure plate or throw out bearing hanging up a little due to rust.

Do you feel the clutch engage? I am not sure on your car but I had a newer one where the pivot point on the linkage was worn out. Some times you could get it in gear and other times it just stayed in neutral. On the road it may grind if it was close. Just a thought of something to check without having to open anything up. The rotated slowly part does concern me that it could be a clutch. As Chevy Nut stated it may need a few runs around the block to sort it out.