I have a 2011 ram with 6.7 I replacedon't the t stat with a 180 my temp gauge hardly goes over 140 my heater hasn't been very warm for a couple yrs that's why I changed tstat what else cold be the problem I had a rad flush 2 yrs ago that's when I started haveing heat issues truck would heat up but it took forever now this winter it isn't getting temp up

 

Maybe air in the system?

 

If you live somewhere cold I believe it should be a 195 thermostat, also a winter front helps lots.