I have a 404 transmission just overhauled but it doesn't shift like it used to. It seems to rob power from the engine. Any ideas?

Check fluid level, when hot and in Park.

Check fluid level, when hot and in Park.
I checked, it's over by about 1/4 inch. Can that cause my problem? If so how do I drain ?

1/4" over is not likely causing the problem at all.

While idling, have you moved the gear shift lever through all of the gears, pausing several seconds in each gear? If you haven't done this, be sure to do it and then recheck the fluid level. Should the problem persist, return the car to the rebuilder for repair.