Since you say you don't know service history, does that mean you recently got this tractor? Have you ever run a reverser before? The reversers do feel a little sluggish when shifting forward to reverse or reverse to forward. It should feel similar when shifting into forward or reverse. If reverse is noticeably more sluggish, then there is probably a pressure leak in the reverse clutch. Is the clutch touchy in forward and reverse both? There are some modulating springs in the control valve that could be broken if clutch is jumpy, or you could have worn or warped clutch disks.