A 743 i had, no matter how hard i tried i could not get it to centre just rite.... I think the previous owner had the pump worked over, the internals looked brand new, no wear what so ever.
Does it just creep a little or does it move a fair amount? With the way the pump is designed, there is a set neutral point, depending on the state of the internals of the pump, centre can be hard to find. If there is little wear the centre can be a monster to find because there is little by-pass between the pistons and any movement off exactly 90 degrees will move oil.
If one side was slower than usual i could say it could be pump or motor related, but faster? not a clue!
Is it the same in reverse? just as fast? if not, its most likley adjustments. Does it turn say to the right going forwards and the left in reverse? That is pulling both levers back or forth together.