To the OP, I know what your next step should be. My story, 1998 XJ.
Aug 2019, hot (RH) side rad tank splits on way home from work. Antelope Valley of Mojave, 100f day, temp goes into the red, 4.0 stuttering, thought I'd nuked it before could get to place for AAA tow. My experience with plastic tanks is that the crimp seal between tank and heat exchanger starts leaking giving warning of an issue, you can nurse it home. This rad had a 4 inch split in tank, Jeep is dead right now. Thought about times in Death Valley, middle of nowhere Nevada, etc. and how bad this could have been.
Bought an all welded aluminum rad from reputable source to kill this worry. Installed new NAPA wp, stat, stat housing, hoses. On 1st drive to work it gets hot at the 20 minute mark. Scenario repeats. Did a lot of troubleshooting without success. With a new cooling system and how hot I had got the motor, assumed I cooked the head gasket.
Pulled the head and took the 0630 to local machine shop for crack evaluation, resurface and valve job. Reinstalled. The Jeep ran great but would still get hot when it should not. To the point it's not practical when the weather gets over 70f.
Checked hose ports to see if I left shop towel in, no dice. Checked for lower hose for collapsing at RPM, all good. Pulled wp to check for correct reverse rotation orientation. Pulled and water boiled a few 195f stats. cleaned AC condensor fins. Vacuum gauge checked the intake, good. Replaced fan clutch. Checked exhaust joints, no leaks. Ran Jeep after warm in dark to check header, no glow.
Thought maybe block is cracked and coolant is getting impinged by combustion gas (I know, no steam in exhaust, getting out there...). Got Jeep hot and pulled plugs, valve cover and rocker arms. Installed plug adapter / compressor, when regulator gets to 20 psi the piston goes to BDC and exposes whole cylinder wall and head. Install spill free funnel and increase to 140 psi, if there's a crack then bubbles will be crazy. Repeat for all cylinders. Nothing - nada.
Three weeks ago spent an afternoon and fixed my Jeep. Now, in daily driving it never gets close to 210. Went to Panamint valley this past weekend, 90's, would only hit 210 when going less than 5mph going on long uphill grades, then the AC fan kicks on and it's cool. Ran the hwys at 70 with the AC on and loaded down, half a hash mark below 210 (high 190's?).
What I did was pull the all-aluminum Mishimoto radiator and replace with the "heavy duty cooling" Mopar 52080104AC, nothing else was changed. My experience only and not a slam on that maker, my particular unit seems to be defective (clogged tubes during mfg process?). Back to plastic side tanks but whatever, hopefully last 15 years before a chance of tank split....
Sorry for the many words.