Thermostat Issue? 2002 6.0l 2500hd

[Taylor2889]

I have an 2002 gmc sierra 2500HD 6.0L that just turned 80,000 miles. the other day i went down to the garage, let it warm up like i normally do and it seemed like the temp guage took a long time to even move of the 160 mark. usually i can let it idle for 10 mins and it will be up to temp. i let it run for about 5 then drove it and it didnt even hit the 210 mark. the heat is hot and everything i was just curious if/when these thermostats need to be replaced. also the temperature was about 40 degrees out.

 

any help would be excellent