I have an 01 f250 with a 5.4 engine. Has a 6 speed trany. When driving most of the time the clutch pedal firm. The other day it took all I had to push it to change gears. Felt like my dump truck manual clutch. Right after that it when back to normal. It has since done it a few times. It will get get really hard then normal. Any ideas why? Fluid good.

 

Maybe a sticking throw out bearing?