without more info (Exact Hub Model in discussion) i think you got the metal mechanical "seal" pressed in crooked, or too far. They rub on the bearings creating excess drag.

look for drag between the cassette/freehub and axle.
this can easily be done by spinning the cassette, sans chain.

an over-tightened axle bearing adjustment can create the same problem, or a "dust shield" is attached to the axle cone, and is then installed too deep........and super-thick grease, or way too much grease, can also cause trouble.

pics of the cassette end of the hub, out of the bike, will help some.....

i just rebuilt a Joytech freehub hub that uses a rubber seal with a mechanical seal, on the drive side... if the mech. seal was even a tiny bit too far out, or crooked, the drag level was unacceptable.