Hydraulic clutch fluid

1996 C1500 with 4.3L and 5 SPD manual. I was driving yesterday and had some trouble changing gears. Seemed to grind during shifting at what seemed like higher RPM's say around 2000. (This was after about 1 hour of driving) I even had trouble getting into gear once in a while. After about 2 1/2 hours or so (vehicle parked) I drove home and it shifted a little better and after some highway driving found it to shift somewhat normally. When I checked the hydraulic fluid level I noticed that it looked a little low. What is the proper level and could a low level cause this condition. Sorry for the long post.

Thanks,
Mark