1970 blower fan speed Heater/A-C

The top speed on my blower fan does not appear to be blowing air at the maximum speed. The force of the air seems to be marginal. I have replaced the blower motor with a heavy duty version, rebuilt condensor
box, all new seals and tubes so there are no leaks. I have replaced the electronic relay on the fire wall. The blower switch inside the car, operates at low and high speed, cuts off in the middle range, so I suspect a dirty contact here. When I checked with other corvette owners in the area, they said the top fan speed on their vintage 70's corvette car was marginal as well.
Any ideas on how to get the full fan speed for the blower?
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Disconnect from the harness and jumper direct to the battery... is there a noticeable capability to run faster that what you get from the harness??... defective selector switch?? restriction in air passages...

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