No heat in pickup?

Winter has come here and I am noticing that my truck is not producing heat this year. The defrost on this used to be able to melt an inch of ice of my windshield within minutes. I immediately thought heater core, but noticed something else weird. The gauge for my radiator is hardly budging at all. This I assume is telling me that my Thermostat is stuck open. Does my assumption sound right about the thermostat, and if so, would the fact that the thermostat was stuck open and not allowing the system to heat up be what's not allowing my heater core to heat up?

Your reasoning sounds good. T-stats usually fail closed, but anything's possible. Certainly a good place to start.
Sometimes another reason for no heat (assuming coolant temp is OK) is an air pocket in line to heater core.

If it is an air pocket in the line to the heater core, how would I go about fixing this?

Thats interesting. The vast majority of thermostats that I have replaced have been stuck partialy open and the complaint has been either no heat or bad gas mileage (low coolant temp keeps the ecu in open loop).

If it is an air pocket in the line to the heater core, how would I go about fixing this?

Easiest way is to raise the front of the vehicle so the radiator cap is the highest point, pull off the cap, set the control to full heat, start the vehicle and wait. Sooner or later it'll start to burp as pockets of air make their way through the system and out.

To easy replace the thermostat it's cheap. If it was only heat it might be a air bubble but since it's the whole system it will be your thermostat they can get stuck either way although closed is most common. I would eliminate the thermostat first because of the price and ease of replacement ( two bolts and a hose clamp) don't drain the system completly just undo the bolts and catch the coolant in a basin then top up later. Tom Canada