Larweber,
I had trouble with my RTV1100 when shifting as I was using it to plow snow. Going from R to L multiple time was painful slow. Took it to the dealer and had them adjust the neutral servo adjustment. It is an allen bolt with lock nut on the right side, passenger side, just above the yellow hst filter. My was off by quite a bit they said. But when I got it home it was still hard to shift. So, I adjusted the servo rod. That, with their adjustment, made the big difference. Do you have a manual?
On the H range no power issue. You have to remember this is a +2500lb vehicle and I think of the HST as an automatic clutch with a 3 speed transmission, L M H, and only 25hp. One Hp for each 100lb. Now if you had a 1/2 truck like the old ones with 3 on the tree, parked it on a hill, would it take off in 3rd. Might but you would soon burn out the clutch.
On the Kubota L is for the hard work, M cruising around and going up down etc. and H, just for the flat easy stuff. They will still pull a good trailer load on flat ground in H but seldom good on hills unless you have a good bit of speed starting out. Even M trying to start off on a hill will sometimes not go. It's the weight thing.
You should start a new post so other 1140 owners will find it easier after you get yours adjusted.