transmission very jerkey in forward gears?

hi! i have a huskee mower ,transmission won,t work properly,very jerkey clunking . i took it apart and checked all gears ,there are no broken teeth or missing parts ,shifter works properly and theres plenty of grease ,its belt drive so no clutch.belt is new .could it be in the axle shafts where the problem is ? it was the only thing i didn,t check while it was open. thanks for any help