Chevrolet Repair: 91 Chevy S-10 clutch, clutch fluid, hydraulic clutch

Question
Hi Van.
My brother inherited a 91 S-10 and it seems to have a clutch problem. The truck works just fine for about an hour or so, but them it becomes hard or almost impossible to get it to go into another gear. Can you think of what this problem is? Its weird how it only has problems after it gets hot.
Thamks for any answer
Mike  

Answer
The problem after it is hot could be due to it slipping, and warping, which would prevent it from completely releasing.

or there could be water in the hydraulic clutch fluid, and it turns to steam when heated, which is like a big air bubble in the slave system. Bleed it.

Van