Oil temp sending units are a very common failure on the Jeep 4.0 engine. And when they go south, they often exhibit the symptoms you are describing.
Some guys temporarily put a mechanical oil pressure gauge where the sending unit resides to verify their exact oil pressure, but my bet is that a new sending unit will restore your oil pressure reading accuracy. It is located directly above the oil filter.
You might want to try cleaning the electrical connector to the sensor with electrical contact cleaner first before replacing it.
I would highly recommend purchasing this directly from Jeep for best accuracy/mating with your factory gauge. Many people including me have had mixed (poor) luck with aftermarket hardware.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!