I only use MMF myself, and my recipe is pretty close to yours, minus a couple of ingredients, and I haven't had any problems rolling it out (I either roll out on a lightly greased counter top, or sprinkled with powdered sugar). If it's getting too dry, it might be because you've added too much powdered sugar when making it. When I make it, I go by the feel of it. When I mix as much as I can in the bowl, I turn it over on the counter top. Since not all of the powdered sugar has been mixed in all the way and falls to the side, I start kneading the fondant, and as I need it, I add more of the powdered sugar. When it gets to the consistency I want, I stop adding in the powdered sugar...regardless if I've used all the powered sugar the recipe has called for or not. I would rather add not enough and have it still be a bit tacky than to add too much and have it too dry. Having it be a little tacky (then I add a very little amount of Crisco to the ball before I wrap it), I then will dust my counter top with powdered sugar when ready to use.
My recipe is rather simple, and is all I've ever used.
16 oz. mini marshmallows...add 4 tbls water, microwave 2 minutes or until marshmallows are melted.
Once melted, add to 2 lbs. powdered sugar. Mix as much as you can, then turn over and start kneading the fondant with lightly greased hands.
That's it! Nothing more added to it!