defective clutch ?

Hello Cross-Country friends, driving a beautiful XC70 D5, 120kW, 2,5l, year 2005, approx. 275000km for 3 years. Finally, I had to find out that especially in the 3.4.5-speed under a mode of operation between 1500-2000 rpm and then impact-like accelerators (gas pedal fully penetrated) first only the speed rises equally abruptly to approx. 2500-3000 rpm and the speed is slightly delayed. So as if the clutch does not fully transfer the force under these conditions If, however, I accelerate from below, i.e. 1.Gang full throttle / 2.Gang full throttle does not occur this phenomenon! A car master spontaneously tapped on the clutch! What do you say, i.e. how high is the hit rate, or what tests could I still do? If I would have the clutch exchanged with a friend, what do you have to consider (have always read of special tool?!) or what should be exchanged in parallel. Do you want to do this. have a good link, with Besc. Hreibung, Bilder? Could a coupler for approx. 220€ from LUK be obtained by car parts, is it recommended, or rather via Skandix? Thank you for your answer(s) ;-)) LG