[davepl]

If you wanted more airflow at low settings you could change the heater fan resistor. Just measure it and replace with lower ohm resistors.

Only thing is they are a dead load - they have to dissipate everything as heat, which is why they're made of coils and directly in the airflow path, I assume. So it's not like you could stick a 1/4W resistor in there. But maybe there are different ones out there. Maybe Cadillac had different ones, who knows? But that'd be the best way to do it short of someone making a fan more efficient at that voltage.