does this sound like a bad thermostat?

[Guff55]

'98 Gran Prix GTP 3800-SC..127,000miles..when cranking cold it takes a while(several miles) to get up to 185/190 on the instrument guage but levels off there..after driving 20-25 miles and getting into several stoplights on a 95 degree day with the a/c on..guage will creep up 2-3 notches past 185 on guage(guessing around 195/200) then will go back down to 185/190 after a few minutes of unrestricted driving..Thanks-David