Jeep Wrangler difficult shifting

I have a 97 Wrangler, 6 cyl, 5 speed. When first starting out the car shifts fine, within 20 minutes or so as the car gets hotter and more shifting occurs the gear shift becomes very tight and difficult to put through the gears. Anyone have any ideas on causes or sulutions?

Check for a clutch master cylinder that starts leaking internally when it gets hot from the engine heat. To do this, carry a bottle of water in the vehicle. The next time the shifting becomes difficult. pull over, open the hood and pour the water on the clutch master cylinder. If the transmission shifts normally, replace the clutch master cylinder.