Where does the pressure screw end up if you just adjust it by the book (turn in until resistance then out 3/4 turn) instead of adjusting it to stop slipping noticeably.
I would adjust the pressure screw distance by the book (engine cold). If it slips, you must then inspect the diaphragm pressure spring, because it may be weak. Does the clutch lever have good resistance when you pull it into the bars. If Yes, then I would say pull clutch pack out (not a big deal) and check the condition of the steel plates and friction plates.