Inaccurate oil pressure and temp sender.

This is in my very clean stock 1997 4.0 with 150k miles. It has the plastic tube style sender

My oil pressure always reads low, and sometimes reads zero setting off the check gauges light. I can rev the engine sometimes and it will read 40PSI and turn the light off immediately. This gauge worked fine, but I broke the sender, and replaced it with a NAPA mexican made unit. Should I get a Mopar unit? I figured it was from the same factory in mexico. I am positive I have good oil pressure. Can I change this to the later style short sending unit? looks to have the same plug, but cant be positive,

My temp gauge will randomly read like its overheating. And then drop down to 210 randomly. I replaced the sender a year ago when I overhauled the entire cooling system. With a Mopar sender in the thermostat housing. This only happens every few weeks. In my experience the XJ temp gauge is pretty accurate. But there is no way this is overheating, and the expansion tank is not boiling. Plus it snaps back to normal temperature after a few minutes. I did not use any sealant on the threads, came with red sealant already on it. (did use thread sealant on my 2000 sensor, no issue).

Its annoying and it freaks out my girlfriend when she drives it, she does not want to blow the engine. Any ideas?

Buy a mechanical temp and pressure gauge and check.

In addition to checking the oil pressure with a mechanical gauge before you hook it up clean out the hole.
Sometimes sludge builds up there and effects the reading.
I put a Napa one in my '00 about 5 maybe 6 years ago. Fine so far.
I even plumbed in some fittings so I could check the with a mechanical gauge and the gauge on the cluster at the same time.
Wanted to see how the readings compared. They were close enough for me.

Check the wiring to the temp gauge too. Wiggle it near the sensor and back where it crosses from the engine to the firewall. I've seen the wire get flakey where it bends right at the sensor, and it's not uncommon for the harness to rub and fatigue at the back of the engine.