Recently my 93 ranger 4x2 has developed a weird issue where the clutch pedal becomes stiff and the clutch feels like it's slipping or will just struggle to engage unless i pump the clutch for 10-15 seconds in which case it feels normal and has no problem starting in first gear... shifting between gears after first there is no problem.

I'm wondering where i should start diagnosing this problem... my guess is a problem with the master/ slave or possibly air in the lines but i feel that should make the pedal lighter not heavier and it's throwing me off.

I would love to hear some ideas on what it could be or if someone else has made a similar thread that I haven't found I would love to know.

truck has ~150k on original clutch.