I used to have to shift @ high RPM 4800 in my moms (stock)73 Nova 4 dr w/a powerglide.
Reason being the rpm would drop off too much when it shifted into second.
It ran a best of 19.6 @ 65 MPH IIRC @ 3000 ft track.
It did not slow down any,, even when I had my 5 friends piled in the car & raced it.
