rebuilt NV-T350 3.55 tanked on me...question

[Jungy]

Ok so I have a rebuilt 3.55 w/ a quaife lsd, prolly 5000 many miles on it since it was rebuilt. The night I was parking my car for the winter This fall I stopped at the gas station my buddy works at to say hi, well I pull into the parking lot in first and I push the clutch in and stop and go to back into a spot. I put it in reverse and let the clutch out and it doesn't make a sound or move at all. The next day I trailer it back to my house and check it out as much as I can w/o dropping the tranny. It goes into all the gears smooth and when I let out the clutch the rpm's drop a little so its engaging. The car rolls while in gear so I'm assuming that maybe the output shaft broke? what do you guys think? I moved and am going to school in grand forks right now so the car is stored at my mom's house in alex so I haven't had a chance to drop the tranny and check her out.