It was the metal shavings from the inside propellers that had eroded away from that orange anti-freeze. The metal shavings had gotten clogged in the bend(curve) in the metal line right before the heater core. Our dude put 20 lbs of pressure through the engine & put some chemical in it, flushed the hell out of it & even showed me about 3/4 of a cup of shavings that had been clogging it. Now you can't even wear a coat inside.
Thanx again to all who had suggestions. Now I'm trying to get my old squeaky serpentine pulley off. I can get my 5/8 socket on it okay, but won't crack loose for the life of me. Does that bolt come off in reverse of regular loosening? (turn wrench to the right? i.e...rightey loosey, lefty tighty???