zippo2341

So about 2 months ago i flushed my cooling system, replaced the hoses, thermostat, coolant etc. I have been watching my temp gauge because its getting alot warmer and humid here in NJ now. After i start up and go to work the coolant tempertaure will rise to about [ C-NORMAL-H ] the M-A area before the thermostat opens then it will dump down to the O. If im cruising on the straight 50mph roads it will stay at the O the whole time. Once i get into town where its 25mph, stop signs, and red lights it will start to rise up again to the M. After i get through the gears get back on a stretch it will work its way back down to the O-R. Is this normal to have this much fluctuation? Im not loosing any coolant, not burning any ive checked my coolant and im at a 50/50 mix ive got the correct cap, water pump doesnt make noise, fan kicks on, everything seems to be fine. Could it be a bad thermostat? should i switch to the 180F? I do have it in 4th going through town maybe spinning 1700rpm could that be not enough? The car has never overheated before, so any input will be greatly appriciated. It basically seems like it gets a little hot sitting at long lights, etc.