From your post I assume you took the whole drive off, if so, did you accidentally bend the gear cable as you fed it through the front of the drive, I mean the section which has a stainless tube sliding into the outer cable. If its kinked or bent it will give a heavy shift. Also is it adjusted correctly, with the gear box in neutral the brass fitting on the cable end should line up with the hole in the shift lever where the cable attaches.
Regards Steve
