Originally Posted by
Aaron Waldron
kma - If the engine is revving up but you still don't have much power, your clutch isn't engaging. You should take the clutch apart and make sure the shoes swing freely on the flywheel pins. Double check the clutch nut to make sure it's tight. Did you clean the oil out of your clutch bearings? Any oil or many cleaners will cause the clutch to slip if you get it on the clutch bell or shoes.
kma, after you check what Aaron told you, also check your center diff. Yesterday my buddy had a similar situation and his center diff was bone dry
I too checked his clutch shoes and even changed them for him as a first response. He went out out and his car had the same symptoms. We pulled the center diff and that is when we found it was empty. Just a thought since we just had this happen to us.