As mentioned before, I planned to flush my coolant now that I know where the drain vent plug is (thumb screw on back of the radiator near the hood latch on the driver's side). I fully drained it, flushed it through with a few gallons of water, and ran it with bottom hose disconnected and coolant expansion tank full of water and heater on to flush the coolant out of the heater. Then I flushed it with another couple gallons of water (bought a bunch of distilled water because I don't trust running ultra-hard Vegas hose water through it). Then I put in a 25/75 coolant/water mix of the orange stuff (concentrate). Flushing it I had the vent plug and expansion tank open which helped it drain faster. Filling it I left the plug open and closed it up once coolant started flowing out of it. After filling, I drove around awhile, let it cool down, and burped it some more as well as filling the expansion tank a little above the top line. Driving around I notice a little bit faster cooling off after acceleration, but it still heats up to about 220F, even when high speed cruising. So far it seems to be running a little cooler.
I didn't think this would solve my issues, but guaranteeing I got all the air pockets out and flushing out the mix I had before with Water Wetter (which I didn't know would gunk up in the radiator) was worth it. It was 117F yesterday and in high speed driving temps went up to 220F and oil temps of 240F. During 70-90MPH driving coolant temps stay under control, but I think the high readings there are due to how hot the oil gets at speed. The radiator is working overtime with such high oil temperatures. The opposite is true with stop and go driving on city streets. Baking at stop lights the radiator doesn't seem to be getting enough airflow. Also, concerning the temp gun readings of the radiator, it makes sense that one side is much hotter than the other. The radiator fan only covers about 65% of the radiator. The other side just has vent flaps on the back side of the shroud.
For those that have either the Mishimoto or the Mountune radiator, I'd be curious to know what average oil temperatures are during high speed highway driving. I have a desolate 28 mile stretch with a total climb of about 1000ft and a 70MPH speed limit on the way to work. I usually set cruise control to 78MPH and even when it's in the 40's in the winter, oil temps sit between 205-218F on the way to work, while coolant stays between 184F-195F. With these 100F+ Vegas summer days, oil temps sit between 220F and 235F, topping out at around 240F.