Overheating XJ, imagine that.

1996 XJ, 222,323 miles 4.0 Liter Auto

All temp findings were held for 10 seconds at approximately 6 inches away from each area.

Okay, here are my temperature findings: Gauge reported, 215, T-Stat housing, 220, Upper Hose, 120, Lower Hose, 182.5 F

First (forward) header tube, 553, next tube, 226, next tube, 329, next tube, 295, last (rear) tube, 289. Yes, I am missing one, but I could not access it, from top, down.

I have a hot cylinder.

Now what?

Rebuild I guess?

Please note:
The entire cooling system, has been rebuilt. Rad, Cap, Hoses, Coolant, Temp Sensor Sending Unit, Thermostat, Water pump. Yes, the clutch fan spins and the Electric fan, works as it should.
Also, I have a transmission cooler, out front and center.

Any suggestions? Please advise...
Thanks in advance!

It sounds like that cylinder is lean. Sometimes a leak on the intake side can cause a cylinder to run hot, or even a slightly clogged injector. pull that plug and the one farthest away from that one and see what they look like.

X2 on that, if all your readings are from the same point on the exhaust. But where did you measure the hose temp? That fast of a drop almost looks like a bad tstat. Also, check temps in the radiator. Use your temp gun, and go across and up/down the radiator. Any big jumps in temp indicate a clogged radiator.