really dumb question
 

I have an 05 with the 4.8 and I have no heat yes I know its been coverd. I have replaced the blend door acuatior and still no heat. Some times it works not great mind you but still works. Whats the best way to bleed the system and if that dosent solve it where should I look next?

Re: really dumb question
 

As the engine warms feel of the heater hoses going into the firewall. They should be equally hot, too hot to hold actually. If one is sort of luke warm and the other is hot that indicates a blockage. Most likely in the heater core. If this is the case disconnect both hoses at the firewall and flush the heater core out with a garden hose or compressed air set down at no more than 30psi. I flushed mine both directions and got a good bit of orange sludge out of it. Got plenty of hot heat afterwards going on 3 yrs now and without dexcool. I use normal old green Prestone.
If yours doesn't appear to have a blockage it may be the hot/cold blend door actuator inside the cab not letting the door open and close.