I've seen some variation between oil pressure sending units. I prefer MOPAR oil pressure sending units purchased from Jeep for the best accuracy/reliability/mating with your factory gauge. The good thing is that you are now registering decent oil pressure so you don't need to worry.
Want to get another deciding opinion? Then go to your local parts store and rent a "mechanical oil pressure gauge" and temporarily install it where the oil pressure sending unit resides. Compare your readings to what you are seeing on your oil pressure gauge on your dash.
The oil pressure spec. for the 4.0 is this:
*Not less than 13 psi at HOT idle
*Between 37-75 psi OVER 1600 rpms
If you're in this range, you're fine. Enjoy your 99.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!