I am wanting to see if any one on here is an AC mechanic. I want to see if you can diagnos a problem from my description and give me an idea on how to repair it.

I'm not but throw the problem out there and see what comes back.

2004 Tahoe. Heat problem. Crank it up to warm it up, no heat. when you get moving down the road the heat will come out of the vents. if stopped at light or idle for a short period heat will go away again. rear vent no heat at all even when moving. I can also tell a difference in temp of the air coming out of drivers side vs what is coming from passenger side. Any ideas??

My guess is blower motor is bad.

Have you checked your coolant level in the radiator? Not just the overflow, but the radiator itself.

possible stuck open thermostat or missing.

sounds like your low on coolant,the second problem could be caused by low coolant also if not then check flow to heater core,grab the hoses at the firewall and see if they are both hot if not you may have a possible restricted heater core.

What temp is the engine running?? If its below 180 at idle after running down the road for a while, then you need a thermostat.
If the coolant is low you should have a low coolant message on the cluster provided the switch is working correctly.
Is there air coming out of the vents at all times when turned on? If not then its the blower motor. Considering the problem is both front and rear I'd say the engine is not gettting to temp.

DING DING DING......WINNER!!

If the controls are set to auto or heat and the temp . is below the setting the heat should come out in the floor. Sounds like a blend door controller or other HVAC control either not working or not getting signal. Don't know if that model uses vacuum or not, most later models use all electric controls. b

Thanks guys, The coolant was a little low, but the coolant light has never come on. I topped it off and it seems to be doing ok.

Glad it's working. And a cheap fix.