Man, I can't remember what years had the internal slave cylinder and which ones were external. My '93 was internal and therefore, it didn't have a traditional "fork" for the throw-out bearing. The bearing slides on the carrier sleeve, but the slave cylinder is mounted behind it - pushing the bearing into the pressure plate. I've since converted it to an external from a '99 TJ since the internal slaves are crap.
None of what you're describing makes much "logical" sense but it certainly must be happening so it's hard to know how to help without seeing the symptoms in person.
If the pressure plate was broken, then it would be like always having the clutch pedal pushed in - no tension on the clutch disk.
If the internal or external slave was leaking, you'd either get temporary use of it until it leaked down, or it'd squirt dry with each push of the clutch pedal.
Same for the clutch master cylinder. But, you'd certainly have clutch fluid leaking out of the bell housing area and/or from the clutch master in either situation.
If you're not seeing leaks, Then it's simply gotta be internal problems with the transmission. The wierd part is that you say you can press the clutch pedal down and it feels normal, but the Jeep jumps forward. This can only mean that the clutch is still bound up with the pressure plate.
I'm of the opinion that you have a bad slave cylinder that is slow-leaking and won't move through it's full travel enough to disengage the clutch. If your's is internal, you gotta pull the tranny. If it's external, it should be easy to check, just have someone press the clutch pedal while you watch the movement of the fork thru the inspection hole in the bell housing. There should be at least 1 1/2 inches of movement.
Hope this helps.