More than likely its the manifolds/risers starting to get clogged, after you replace em you should see improvement.
Raw water has to get in (impeller and circ pump) and it has to get out (thermostat, manis/risers) anything that gets in the way of raw water flow will make you run hot...
The spec on my OMC stat is it starts to open at 160, is fully open at about 180, but in my experience, this engine runs from about 165-170, when coming off plane, it will heat up to about 175-180 and then cool down. This is with a new impeller, new stat, new circ pump, new mani/riser units (OMC Batwings) and new hoses. Engine is an original raw water cooled 4.3 from '88 so probably a bit of rust inside

....next engine will be closed cooled for sure...
after you replace the manis/risers, get an IR heat checking gun from radio shack, and keep tabs on your normal temps, then when they start to get a bit hot, you will know it's time to check em again. In Fla salt water that could be as short as 3 years, mine were just starting to clog here in Long Island with only a 6 month season after 5.5 years....