the higher temps at freeway speeds and lower temps in town could possibly indicate a blockage in the radiator.

Bring it up to temp and turn it off.
Stick your hands into the the shroud and feel for cool (a relative term) spots.
is you have uneven temperatures a rod and boil might be in order or a citric acid flush might get some more efficiency.

you should be careful when you do this.

you might have air in the system too. that causes wacky temp fluctuations