Well I was driving my truck yesterday stopped at a stop sign and took off again went to shift into second and the trans would not come out of first. Tried putting it back in first and it feels like its blocked. I can put it in all the other gears but its always in first and if I try to do it while I'm moving it just grinds. So how hard is it to rebuild a nv3500 and are there any special tools required and where can I find parts?

 

I'm hardly a transmissions genius but it sounds like your linkage is broke

 

How does the pedal feel? My slave cylinder went out, had similar symptoms.

 

Pedal feels normal. Clutch was changed 3k miles ago. I'm thinking I may have broke a shift fork but I'm not sure

 

Sounds like time to open it up, and have a look. If you haven't done this before, just make sure you keep track of what goes where. Pictures of the process are very helpful here...... take your time, do it right. Find out what's broke, and fix it.