I did not replace the radiator until I went to the mishimoto. So the radiator probably isn’t your issue.

of course the coolant would sit with a t stat. As it should. If it’s 108 outside your car will start at 108. And then it will hit 195 and the therm will open. It opens gradually allowing coolant to sit for longer at the radiator before fully open. If the coolant is being partially restricted at operating temp as it should be, it will be getting exposed for a longer period of time to air moving in front of it at the radiator; and therefore cooler by the time it reaches your engine. You should always run a t stat. But that may not be your issue if you were already overheating. However you won’t know if you’ve fixed the problem if you’re still overheating due to no tstat.

I think you have a blockage somewhere. Sometimes you have to flush these things 10 times. It can be at the heater. It should burp on its own for the most part. On older systems you need to let it run with the cap off and the heater blowing. Speaking of which, are you getting choking hot heat? Check at night when it’s cooler. It should be blazing hot at full blast when your engine is up to temp. In your climate you need an aux trans cooler. The hot trans fluid in the radiator transfers heat to the coolant nearby.

Good luck. This drove me crazy. I never overheated while driving, but at idle and low rpm it would
kick up to 225 before the aux fan could control it. My process was:
reverse flush coolant many times. This helped slightly.
replace fan clutch. No help.
replace aux fan. No help.
replace both temp sensors with dealer parts. No help.
replace old crusty ccv valves. No help.
replace many rad caps.
flush and burp the **** out of the coolant again. No help.

replaced t stat w dealer 195, dealer water pump, and replaced the mopar hd cooling radiator in there from PO with mishimoto aluminum. Now sits at 210 like a rock in SoCal summer. On desert climbs in 4x4 it will rise a bit. 220 is ok. On obdii it’s even cooler since the temp sensor for the computer is at the front of the engine. In fact, once it hits around 210-12 at the gauge, the temp will actually fall slightly back down, even at idle. That’s the t stat opening up more, and the cooler water rushing in.

I have a stock mopar trans cooler that was part of the towing package.

Before this odyssey I would regularly hit 223 at idle or higher. Once I hit 235 on a climb and decided that was it time to pull the rad, pump and tstat. Never had an issue since and I’m running the xj clutch. Now on long climbs I can hit 220 or so but I’m talking 7k feet of climbing nonstop at low rpms, on unpaved hardpack and washboard with my tires at 12-15psi