Right now my f150 will heat up like normal in a few miles and the heater will work great after about 5miles the temp gauge will drop and the heater will blow cold air. After a few more miles the temp gauge will peg out at hot and a warning light comes on. Changed the thermostat last winter

 

Sounds like your thermostat is sticking. Open and then closed. Take it out and check it in a pot on the stove.

 

I'll give a try. Maybe I got a bad thermostat

 

Sounds to me like your cooling system is low. Check that.