Had similar for a few years not slipping all the time but when nailed about 7k it would rev up then "catch" and it would be fins. After putting it on a dyno at Skegness and failing to get a run out of it with out a slip I decided to sort it. New friction plates and HD springs problem sorted went to Silverstone two put with some acceleration "testing" on the way did not miss a beat easy to change (fist time for a clutch) took about 3/4 hour just taking my time did the filter and oil at the same time no problems at all. Bite the bullet and do the clutch.
Have a look at this, it's quite informative
I think you want to change the oil anyway if you are changing the clutch,,,