2008 Ram 1500 5.7L Overheating

My eingine temeperature starts out normal, then after about 20 minutes of highway driving the needle climbs to the high side. I turn the heater on to control it after that, but it stays running hotter than normal. The radiator fins have been washed free of debris, coolant level is visible in the resevoir, the fan spins and I just changed the thermostat. Used a laser thermometer and only got 205 as the top temp. Any ideas?

is it blowing water out to the reservoir? You may also have a faulty sensor. next is to check to see if theres any faults in the ECU.