Freelander TD4 clutch

Hi all, Purchased my Freelander in December on private sale, had couple of problems but very pleased. Noticed on Friday that clutch seemed to be slipping when in 4th or 5th gear. Seemed very strange that when you were normal driving and came to an incline on tarmac gave it some throttle revs increased but speed did not.
No problems engaging gears, and cannot make it slip from standstill engaging any gear. Any ideas would be much apprieciated. Thanks

clutch slipping at peak of greatest load

So looks like new clutch then ? Thanks for your reply freelance