I have a strange one:

I've been noticing lately only when I'm in 3rd & 4th gear that my RMP raises fast then rides out Almost like an automatic trans slippage. But my trans is a manual.
For instance: I push in the clutch and put it into 3rd gear and release the clutch & give it gas, it acts fine. Then I give it more gas and the RPMs raise fast from 1500 to 2400, then slows to 2100 for a bit then raises again. During this time my MPH is rising rapidly as it should.
I don't believe it's the clutch since it happens afterwards.

1995 F150
300 ci 5spd 4x4
184,000 miles

Any help is appreciated.
Thank you

 

It can only be the clutch.

 

I also drove this down the road for a mile and kept it in 4th gear. Then slowed down to make a turn without shifting and pushing in the clutch. After I made the turn it happened again. Could this still be the clutch?

 

It's the clutch.

 

clutch slipping.