Heat and air

sound to me like the fan isn't working from what you stated. if its now then the front blower motor resistor has died, very easy to change they are in the passenger foot-well just below the glove box, i say that because you said you feel cold air when the windows are open, this creates a vacuum effect and pulls air through the vents so you feel ac and should be able to do the same with heat.

Thank you

My heat is really weak in 05 5.7 what could be causing this problem

@Ctkbennett your either low on coolant, the heater core passages are blocked, or the damper door in the hvac assembly is stuck on cold so long as the engine is up to operating temperature (if its not then it is most likely a thermostat issue). I would start by checking the heater core lines on the firewall to see if there both hot or if one is hot and the other is much colder this would indicate a restriction to flow aka plugged heater core. Assuming that both lines are hot and the truck is up to operating temperature then you have a damper door (blend door) issue.