Adjusted clutch slipping again

Hello. I used to be on here few years back. Since then i forgat my user name and password. Would visit to to read forum.
Many of you were more than helpfull before and i need help/ advice again. My clutch started slipping ( manual , eaton 10 speed) in 9th gear few days later in 10th as well. Only slipped from 1300-1500 rpms if i took it easy on the throttle it would not slipp I took it to my shop mechanic looked at it and said more than 50% left on the clutch just needed adjustment. He adjusted it i ran over 1500 miles no slipping. Then today it slipped 2 more times , maybe a 100rpms jump i barely noticed it. So question is why would it slipp again. Iv lost clutches before , wouldnt go into a gear , slipping real bad , woudnt pull iv never expreienced nothing like this before.
Thanks in advance

 

Thanks for reply. Im definitely replacing as soon as i get back. I just dont know why would it slipp again if he was able to adjust it and it was fine for around 1500 miles.

 

Ill have it checked for adjustment. As soon as it started slipping i took it realy easy , trying to prevent it from slipping. I think i did more than ok job slipped around 10 timed in over 3,5k miles. Cluch is fine , releases like it always has, smooth shifting.