Temp Gauge fluctuates from 150-190 and back

Hey guys, I've been chasing down this issue for a few months now, and haven't made headway. Looking to see if anyone has had the same issue.

96 XJ 4.0 AX15.
New oem style/single row rad (~5 months old)
New (cheapest) 195 thermostat (~1 month old)
Water pump ~2 years old
All air burped from the system when tstat was replaced, coolant levels are full.
Hyline hood vents (these things are huge if not familiar with them)
Temps have been between 40 degrees and -10 degress here in PA, regardless of that though the temp still fluctuates to the same degree

This problem started when I replaced my leaky old rad with the shiny new one. Prior to replacement, temp would hold between 190-210 steadily in all weather conditions. After replacing the rad, the temp now rises to about 200, then the stat opens and drops it down to the 150-160 range. Jeep heats back up to 190, and then the temp drops again to 150-160. Rinse and Repeat.

I thought it may be a stat, so i threw in the cheapest 195 the parts store had. Didn't go the cheapest by choice, it was the only stat they had in stock. Is it possible the cheap stat is somehow faulty, causing the temp to fluctuate like this? The stat i had in there behaved the same way after i replaced the rad..

I've blocked off the hood vents and the mech fan side of my radiator with cardboard, but this hasn't had any effect on the cooling at all. I'm pretty well stumped and don't really want to throw parts at it without knowing what may be going on. Thanks for any help guys!

Here on the east coast it has been cold for the past few weeks.
My XJ does the same it takes about 20 min at highway speeds before the oil pressure and water temp return to their normal positions.
Mine has done it with Mopar,NAPA,Stant,MR.Gasket high flow,MotoRad, and other name brands. Keep watch on coolant level and drive it.

When my 00 did that, a new top quality T-stat made it run at a steady 195-210*, even at -10 below zero.

^^ this. My 01 was the same when I had a failsafe. A Mopar thermostat fixed it.

Good stuff, looks like a Mopar stat is in my future. Thanks guys!
Hoping once this issue is fixed my mpg goes back up from 12 to 15, thinking the Jeep is constantly in warm-up mode, maybe dumping fuel. Who knows, and really what do I want out of an 18 year old Jeep on 35s haha.

With the dealer stat, the jiggle valve goes on the top.

Stant Superstat

Hey I have the same issue. Tried the 4th t-stat yesterday but it is all the same. Temp goes up and falls down when the t-stat opens...on and on