Sounds like it may need new friction plates
If its slipping at high revs and its an '05 with high...ish Ks chances are the friction plates are all used up.
Unless the prev owner has re newed the plates and make the beast with two backsed around with the lever adjuster screw ..... unlikely.
Not a big deal wet clutch you can do your self just add $$ and some elbo grease.
It wont dump all the oil when you open it up ,some but not all so best not do it in the living room
or on the terra cotta tiles around the pool.
Plenty of wet plates on ebay or check Gowenlocks etc just watch you dont damage the gasket .