When your coolant temperature starts to rise like that, turn off the AC and see if it starts making a difference over the course of the next 3-5 minutes of driving. If you notice a change, and this vehicle is used regularly for towing in the summer, you may wish to consider looking into an electric water pump that runs full flow regardless of engine speed. They will be expensive, but in my own personal experience, they have been worth every penny.
Case in point, after modifications, my Grand Marquis was undriveable during the summer when ambient temperatures routinely range between 105°F-125+°F. Regular driving on the freeway at speeds to 55 - 75 MPH would result in coolant temperatures ranging from 215°F-230°F, sometimes higher, even with a 180°F thermostat and a tune that configured the electric fan to come on full blast at 206°F. It also has a custom, all-aluminum radiator and a high flow OE water pump from a Lincoln Navigator. I also looked into a Stewart EMP mechanical water pump, but a lot of folks had similar results with this compared to the Navigator water pump. Turning off the AC would drop coolant temperatures back down to the 209°F-220°F range, but that is still hot considering the temperature range this engine is supposed to be operating in. WOT was completely out of the question, because detonation would start to become an issue even under light throttle.
What really helped my situation was switching over to a Meziere electric water pump that constantly flows at a rate of 55 GPM. Coolant temperatures now range from 200°F-204°F at highway speeds. I realize a lot of folks will be turned off by the "electric" part and the initial cost; that certainly was the case with me, but then again, fuel pumps are electric as well and generally tend to last a reasonably long time. This particularly unit has a lifespan of "3,000+ hours" according to the manufacturer, although the 3-4 year mark is what I'll consider as its service life to prevent unexpected failure at the worst possible moment.