99 jeep wrangler

It will lack lots of power going up hill, especially if its a really steep one and you keep it in drive. Make sure you downshift to second, or fist if its really steep.

Check engine light on or flashing ? Engine misfire an you fried the catalytic converter but that is just a guess without testing . Can't help you don't have a lot of money . Your best option , take it to a qualified repair shop an have it tested properly .Don't guess ,test .

It is likely leaking at the slave cylinder

Get the clutch slave cylinder and master cylinder looked at.One of the 2 has failed.If the pedal goes to the floor or is very loose,this is very likely the cause.Not an expensive fix.Hope this helps

yes thats what it sounds like....Cant really be sure. Seems like you know your Jeep go with your first choice.

Has this Jeep been modified at all?
It sounds like the shifter cable was reinstalled backwards.
Specifically the 4-Low "Not Climbing Well". 4-Low should give you the best torque and hill climbing ability.
Do you feel any "Binding" in the steering wheel (difficult to turn)?
Remember a Jeep uses real driveshafts and differentials to give you 4WD - you cannot engage 4WD or 4-Low on dry hard surfaces. It needs a little bit of slip between the wheels for turns.
Check you're fluids too.

in a perfect world, computers and related systems are a great addition to the automotive industry...But, You would not dream of using your PC in the backyard, in the rain, snow and searing heat. Yet the system in your car is asked to do that daily. (would be nice if a little button like on a chicken would pop out of a failed component to tell you it's not well.....Your guesses are valid, but before you go out and buy parts, have a code scan done and see what's there. Codes give you a direction to begin looking, they don't get really specific, but when added to what you already see and know can be very helpful. Fuel pump problems don't show codes though so you may need to do a pressure test. CPS will sometimes throw a code, but they can also cause strange problems without doing that. The largest problem I see right now is that it starts right back up, giving you no time to do testing. The random on/off thing suggests the possibility of a bad connection either at the computer or ignition switch. You can try wiggling the harness a bit and see if you can get it to stall.
It would not surprise me if it took a while to find this problem as this is the type of thing that drives even good shops crazy.

check clutch switch and starter relay in the power distribution box near the battery. Likely one of them has gone bad. Tell me what you find.

Sounds like you may have bent a shift fork or your cluster gear has some missing teeth on it now. I would venture to say that is it a bent shift fork. This will require the transmission be removed to gain access to inspect and repair.

If its using a lot more fuel than usual its almost garaunteed an 02 Sensor. Those are located on the Exhaust Manifold's, are about the size of your thumb, and generally have 2, or 3 wires coming from them. If you can, check them for operation before you replace them as sometimes they're kindof expensive.