A couple of things to consider when working with hyds clutches..
Cutch facings get Glazed from operator riding [ like brake riding]
and hill holding. A glazed clutch will slip like hell, no matter how thick the facing , specially when hot..
Clutch flex hose can constrict [ again, just like a brake line], and act as a one way valve.. you can push the clutch in with the high pressure of the master, but the RETURN pressue is from the spring of the pressure plate,, not much, in comparison, specially as the plate gets to its full engaged end..so, a restricted hose can cause a slipping clutch..[ there is a pedal return spring , but nil effect on this factor]
A test here is to have someone push/release the pedal and then you immediatly open the slave bleeder ...if the slave is still under pressure w/pedal up, you have a restricted hose..that will usually slowly bleed off.
Usually, a worn clutch will both slip and catch higher and higher as it wears.
And sometimes , it is just a combo of slight glaze disc, worn plate surface [ heat checked] and fatiqued pressure plate springs.
A good rule is alway replace all three [ plate,disc,bearing]