I would test theold and new thermostatstoo.

you can put them in a pot on the stovetop and warm them up...you need a thermometer (doh).

watch to see what temp the thermo starts to open and then temp when it fully opens. In theory, a 180 stat should be fully open at 180.

So on the highway you are maintaining that fully open state of 182 or so. Round town your partially open and running lower temps. If this is whats going on,you got no problems. But you are right to be suspicious cos its more likely to be the other way round.

 

It could just be how the engine generates heat relative to driving conditions. Check the sensor/gauge but it sounds like it's prolly fine. You might wanna run a 195 stat though, you get better combustion when you're running hotter so long as you don't have to sacrafice the tune or develop detonation.