Is this an automatic shift vehicle? Or manual valve body? Either way, sounds like you have to start at step one. Check the shifter linkage. That can cause all kinds of issues. Then Check fluid level with car off in park. Note where the fluid is at on the stick (it should read high from sitting due to converter drain back). When it’s running, check it in neutral. See if it’s pumping fluid through the transmission. The fluid level will drop on the dipstick. If it’s pumping fluid properly and the fluid is full, the pump is moving fluid through the transmission. But since you have a total neutral box, there are so many things that can be wrong. Sealing rings could have been left out of the transmission. Which would be very weird or rare, but if it was rebuilt and then sold to you, it’s very possible they missed something. My suggestion is check the easy stuff first, shift linkage and fluid level. If everything is hooked up properly and the trans is pumping fluid, a pressure check at the governor (if automatic shift) and servos would be next step. If trans is showing no pressure with everything hooked up properly, trans will have to come out and be gone through. No pressure means no movement. I hope this helps get you started.
RJ
