While cranking the a/c lately, the air has been freeeeeeezing cold coming from the vents. But, when I hit the gas, the cold air comes out of the defroster and the floor, not the vents... Obviously, nothing changes on the ECC either...

Sounds like a vacuum leak. Now the question is where....hopefully one of the guru'* here will let you know where to start looking.

Hmmm, but you also have climate control. I don't know if the direction/air flow door in the climate control is vacuum based (I don't think it is).

Right, I didn't think it was, either (at least not on the electronically-controlled models), although certainly the symptoms suggest that that'* what the problem is.

In any event, when you get on the gas, your intake manifold vacuum temporarily plummets. In order to prevent endless cycling of the HVAC outlet settings under those circumstances, there'* a vacuum reservoir/booster under the hood that acts to cushion the system against vacuum fluctuations, and includes a one-way valve to prevent loss of vacuum from the reservoir when intake vacuum drops. On most older GM cars, it'* a black plastic sphere about 6" or so in diameter, mounted near the right (passenger'* side) hood hinge. On the later Bonnevilles, it'* a large square black box mounted on the firewall between the master cylinder/brake booster and the end of the MaxiFuse/Relay Center cover. In either case, you can easily spot the vacuum lines going into it.

So check that out under the hood and see if everything'* tight, not leaking. If you hear hissing noises anywhere under the hood or behind the dash, something'* letting air into the system.

sweet, thank you!!!