Donno of any "tractor" gear-type transaxles that are built for much
on-the-go shifting. The Hydros might fit your speed requirement by using
larger diameter wheels or, to a small extent, altering the input speed thru
an over-drive device of belt or chain drive.
A suggestion might be for you to "cruise out" your area golf-cart dealers
and such . . those gas powered carts have some neat driveline goodies that
sometimes land in the scrap pile.
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