So my jeep used to run perfect with zero issues until one day it started overheating and then my check engine light came on so i hooked it up to tester and come to find out my oil cooler was bad. I buy the cooler and replace everything then about a month later my engine light came on again and this time its my damn oil pressure sensor witch is located directly next to my oil cooler.. SO back into the bottom half of the engine I go, Now everything is fine It runs great but for some reason when I'm at high RPMS its acting like it wants to overheat again but the second it shifts my temp gage rapidly goes back down to normal. I have no clue what could be causing that to happen. Iv taken it on 5-6 hour drives and its been perfectly fine with no issues but its very strange the minute I'm stuck going up a incline and its keeping my RPMS up it wants to over heat and I will have to let off the gas till it downshifts and then get back on it and the temp gage with go to normal after spiking..

I drive a 2013 3.6 with about 145k on it

 

My ZJ had a similar problem. Previous owner put stop leak in the radiator. Even though I changed the fluid, it still clogged the radiator over time. It was a slow death for it. Higher rpms means it will need to push more fluid through the radiator. If there's not enough flow to cool the incoming coolant, the temperature will start to rise. I'd change the fluid and inspect it first.

 

Is your rad fan operating?
Our 02 WJ had fan and fan relay go kaput causing an over heat. (I think the bad fan motor and hi current draw also caused the relay failure).
It ran fine when travelling but in town and hi load and heat situations it would heat spike.
No idiot lites indicated the fan was not functioning. Had to self check. Let idle for while till heat rises, and rises, and rises. Don't let it boil over!
Does running your heater full blast bring the temp back down?
Best to check your fan operation.