Welcome to the Brotherhood of the Busted Axleshaft! Sounds like either a snapped shaft or stripped splines. Either can and does happen fairly frequently on well-used trucks. The 10-bolt is a semi-floater, so the shaft may or may nor come out. I'd pull the passenger side shaft and see what ya got in there. If it's just stripped splines, stick it back in, drop the rear shaft and lock the front hubs for a while. If the shaft is broke, it can wander out on it's own and leave you doing the tricycle thing going down the road. That sucks...done it twice over the years. I'm not sure if your 10 bolt is a C clip or not...they made them both ways depending on the year. If it is, it's likely stripped splines...which is the most likely.