My engine temp gauge won't get above ~150. When the truck should be up to temp (190) it just hovers around 150 and sometimes even goes back down if I haven't been putting much fuel to it. Just a busted gauge?
-I JUST had the starter replaced if this may have anything to do with it.

 

sounds like your thermostat is stuck open. Try replacing that. I have heard recommendations to only get the cummins thermostat as they have the best track record. This site has the cummins thermostat. It would be an easier swap out then a new gauge.

swordfish