Help with diagnosing slipping clutch.

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All wheel drive, manual transmission, 2.0 liter engine, 200,000 miles. Acts like the clutch is slipping especially on inclines. Ne visible fluid leaks, and the slave cylinder functions when the peddle is pressed. Peddle linkage and bracket look ok. Bled the clutch slave cylinder which helped with peddle feel and engagement, but it doesn't engage well if the clutch is let out slow. Takeoff is better if the engine is revving and the clutch is dumped. Could anything like the master cylinder, slave cylinder, transfer case or differentials also be the cause? How would I verify the clutch is needing replacement myself? Thank you for all assistance!