Heater issue

[Jmarch]

2000 silverado z71 5.3L ext cab LS about 120,000mi.

 

When the heat is off (but still turned to hot) or when I have it on "1" the heat coming out is so damn hot it almost could burn your hand. Turn it to "2" the heat is a good temp and air flow increases, like it should. Turn to "3" and the temp goes down a bit and air flow increases. Same goes for "4" and when you go to "5" the heat almost doesn't exist but blowing like a damn hurricane. I figure it can't be a blockage since the air flow definitely increases. Heater core can't be bad since it DOES blow hot. Winter is quickly coming up here in NW Ohio...any tips advice suggestions help is greatly appreciated!

[gmtech4]

its plugged inside ,but letting some thru it ,the air is taking all the heat away on position 5,the coolant cant keep it hot enough

[Jmarch]

So does that mean the heater core is clogged? If so, what isto my next step? Or just clogged somewhere along the venting somewhere between the cabin filters (which are new, the old ones were pretty nasty) and the vents?

[txab]

Start by flushing the core

[gmtech4]

backwards