GM_Guy - Whats the point of turning on the heater? There is no heater core shut-off in these cars.
If the heater core is plugged
there won't be any, or reduced, heat out of it. The fan on -max-
will sustantiate that.
gDMJoe - Did your coolant system flushing include having the heater set to the hottest setting and the blower on high with the engine running?