[dangerous]

I'm going to put my money on a flow problem in the area of the radiator. A lower temp thermostat and thermo fan switch certainly can't hurt, but I don't think they are going to solve your problem. If you're running hot at highway speed, you're fans are not going to help you at all (which makes the fan switch irrelevant). Unless there's a blockage in front of your radiator, you're getting all the air you need at highway speed.

if you have an A/C condenser (i.e. you haven't yanked out the a/c system) I would check to make sure this thing isn't full of debris and blocking your air flow. I'm not going to tell you to yank it out and lose your system charge....but you might be getting close to that point soon.

The other area of "flow" obviously is the coolant. If you're getting temp readings on both sides, your thermostat is probably opening. If you are going to be digging that thing out anyway, make sure you check it in a pot of water before you install it just to make sure. Another thermostat tip is to drill a 1/8" hole at the top of the flange when you install it. Helps with bleeding out air.

One more thing, since you'll be draining your system to swap your thermostat, it's a good time to pull that radiator out for another look. I know you said it was new, but you might run it down to a radiator shop and have them flow test it just to make sure there isn't something inside blocking the flow. Your symptoms sound a lot like blocked radiator flow to me (despite being new) so it might be time to look at some less common possibilities. Could be foreign matter (perhaps from shipping) packing peanuts, plastic, gunk or sludge from a hose, dead mouse, etc that found a nice spot to rest in your radiator.