Hey all, new user here. So, if there is already a fix for this please redirect me.

Truck takes a VERY long time to warm up, once it does the temp. gauge is right where it should be. (Just short of center.) However, if I'm moving uphill for a good amount of time, or WOT getting on the freeway, she starts to get hot. It goes back down to normal fairly quickly once it's not stressed anymore.
I've changed the thermostat 2x with OE mopar, new water pump also OE. I've changed the fan clutch, and radiator cap.
Pressure tested and had a leak at the reservoir, so that's also new. I've vacuumed the air from the last coolant flush and added coolant via vacuum. I've done a "burping" procedure every way I can think of. Please help if you can. I'm about to just burn the damn thing down at this point. Thanks.

Edit: Once it's at operating temp, it can idle for hours without any issues. But, letting it idle to warm up takes a solid 30-40 mins.