Chetmotox, how did you "burp" your system? I have pretty much the same delema, and it's darn cold here in Western N.Y. state on my way to work @4:20 am, so I I know where your coming from!
I don't think my heater core is plugged or restricted, because I flushed it with a garden hose and it flowed decent and flowed clean after about 5 minutes. Plus the heater core area of the plenum in the cab feels warmer than the air coming out of my vents.

 

Park with the truck's nose uphill, the steeper, the better. And, I even used ramps. Then run the engine for a bit, goosing the throttle from time to time.

 

HeyYou where abouts should the flush T be mounted in the outlet line?

 

Dbbd1, while the trucks up on ramps and running the radiator cap should be off?

 

In the heater core outlet line, as close to the heater core as you can get. Right after the bend where it comes out would be good. Basically, the highest point in the line.

 

Yeah, cap off. Make sure that you leave it up like that long enough that the engine warms up enough to open the thermostat.

 

Ok, thanks everyone! Looking forward to trying to "burp" the system. We had a couple days that were like 59° and up last week, wierd thing is, my heater was working GREAT those days. I hate these intermittent problems!!!

 

When I tried it yesterday I wasn't on much of an incline so I'll have to try again today.

 

The incline for attempt #2.