The Kohler Command twins all typically burn about one gallon/acre when mowing. That's typical across the board with any gasoline powered machine. As far as scalping goes, some high spots will scalp no matter how the deck is adjusted. If the width of the high spot is less than the wheel base of the deck, it's going to scalp. With the 44", you do need to make sure the deck 'hangs' and doesn't ride the ground. You also want to make sure the deck is very slightly nose down and the gauge wheels are adjusted so they don't bang around on the ground. As far as the trans leak goes, is it on one of the bolts on the vertical split? Some thread sealer would fix it. Sad, but that's probably all the dealer would do.
Joel