Unfortunately what you describe is often the first symptom of a clutch throwout bearing failure. That part is around the main shaft between engine and transmission and can only be serviced by seperating the transmission from the engine, which is complicated by the transfer case and two driveshafts.
You had best plan for a new clutch in the near future. That would include a new throwout bearing, new clutch plate, and new cover. Most times it also means a new flywheel (because it can't be resurfaced without losing some life on the new clutch).
If you have done a clutch before, even on a 2WD vehicle, you will probably succeed. If you have not, then the TJ is not a good place to learn the basics, and you either need to find some knowledgeable help, or have a mechanic do the job in his shop.