Why does My 1999 jeep stalls at any giving speed then starts up by itself...

SOURCE: Jeep stalls ata speed with clutch depressed.

Not being there makes this difficult to give you anything useful, however, in reading your post, It makes me think that the clutch has little to do with the problem. Likely, the engine is either not getting enough fuel or is loosing spark. When this happens, the clutch being engaged is keeping the engine turning...when depressed, it allows it to completely stop. I would first check for proper fuel flow and pressure (filter & pump), then check ignition (crank sensor & other related ignition components) The items I've specifically named are the most common ones that fail. You should verify with individual component tests as well as code tests (larger parts houses do testing free) before replacing suspect items or repairs can get very costly even when not using a repair shop.
The tests etc are too involved to write here, but are outlined in vehicle specific manuals made by haynes, chilton etc.
If you need help on specific items, I can help you with that.
good luck!