Thermostat could be sticking or and air bubble in the system. Food for thought: Living in SoCal and traveling to the Colorado River and Baja I see temps upward of 126 degrees with long freeway hillclimbs (sometimes towing) frequently, so.......soon after purchasing my 18 and discussing my disdain for the shutters with the local Ford dealer they informed me that Ford told them (dealer) on a couple of hot running trucks to actually remove the shutters (true story). Anyway I installed a 170 thermostat and removed the shutters and turned on the temp numbers above the gauges. Immediately after install I saw erratic temps. So i parked the truck on an incline and opened the coolant reservoir and turned on the heater then brought the truck to temp. It helped but had Ford check it out anyway because they told me there could still be a air bubble in there still because there are a couple of valves in there that if you don't open up at the same time you won't properly purge the system. Ford checked it out at my oil change and said all good. Well after after 30K miles of driving on the 170 thermostat the truck runs at 196 at freeway speeds, a little more passing or hills then right back down and if you coast down a hill or come to a stop the temp will drop to almost 170 but once your back on the throttle back to to 196ish quickly-(I never changed when the fans come on). Driving in temps plus 110 degrees and I see 201-203 with drops below 180 if coasting, but right back up when on the throttle again. Sorry for the long post hope this helps, also the numbers above the swoop gauge tend to show a wider difference in temp then represented in the swoop indicator.