Issue with heat
 

So I'm driving to work this morning at 330 and it was about 28 degrees and the car took a little while warming up, but it never really got to warm and when I came to a complete stop it got cooler. When I got onto the highway it started blowing really hot air which seems what it should have been blowing. I am thinking that it is the thermostat. Suggestions Thanks

yup pretty sure its the thermostat