225 running a bit warm!!!

Hey my slant six runs at 201 Degrees with a 180 thermostat and if I'm on the highway if running about 75 mph a bit higher like 215 or so but if I let off the gas it goes back down just wondering is this normal or what? I have a new thermostat, radiatior, water pump, checked for small leaks nothing that is out of the norm. hoses seem good to, even added water wetter. Temps been close to the 100,s here in MO lately!!!