super major gearbox problem?

hi all, never first time user of this site hope somebody can help. My super major gearbox gets quite hot on road runs, it feels nearly like da brakes are half on. I removed the box and checkd the handbrake plates wasent sticking and they're fine. 2 bearings on either end of the top shaft at the rear of the gearbox had rollers missing so i replaced the bearings. And refit to tractor. I havent drivin tractor yet but theres one thing that confuses me still, when i jack up rear end of the tractor and try to turn the two wheels foward together its very hard to turn, i removed foot brakes to eliminate them and its still the same. 1 wheel can be turned no problem but when the crown wheel has to turn the gearbox shaft its very hard. Pinon and crown wheel turns fine when gearbox was removed. Also when input shaft is turned by hand in the bell housing its quite easy to turn everyting with a gear selected in the box, but very difficult to turn from the back towards the front. Can anybody help me??