After getting done putting new syncros and upgraded shiftforks in my tranny, I got it back together and spun the mainshaft by hand. It only turns one complete revolution then stops, doesnt matter what gear or in neutral it stops like its hitting something. I took the main case off and could see anything that would make it stop turning. Has anyone came across this problem or anyone no what could cause the mainshaft to not spin freely?

 

Sounds like you have a sticky 4th gear syncro ring. Put a litte grease on the ring and that usually solves the problem. If you fill it up with fluid, it should fix it as well.