Puzzling 1997 lumnia 3.1 overheating problems.

I'll try to lay this out as eloquently as possible, although this has been quite a complicated ordeal.

Apprx. 1 week ago My 97 Lumina with 132,000 miles started having problems with the heater alternating between hot and cool air.M (coolant level is fine)
The next day however the car started overheating.
Here is what I've done so far:
1. As the temp guage on my Instrument panel raises and goes in to the red, my heater blows cool air, then out of the blue the guage will drop and the heater would blow hot air. This sounded like a thermostat problem so I have sience replaced the thermostat but it didn't fix anything.
2. Next I noticed that a radiator hose was colapsing when the engine would excelerate so I replaced both hoses, the water pump and drained and refilled my coolant system. I also flushed the heater core, and bled the coolant lines. Still nothing fixed.

Here is what is puzzling, at idle the car runs fine and does not overheat, as well, the heater blows very hot air. However when I drive the car it overheats within 5 min, the heater blows cool air, and when I stop and bleed the coolant lines there is a bunch of new air in the lines?

I don't know what to do next. All this sounds like a blown head gasket? Or cracked head?

One more thing, the lines going to and from the heater core are very different in temp and I haven't checked the vacume control yet. I realize this could be the cause of the heater problems, but could that actually be what's causing my overheating?

Thanks for your help - Jordan