I have it on our 2012 Lexington, and wouldn't be without it. Hugh improvement in tranny shifting. Does make a bit more HP. Fuel usage will remain about the same...you'll use a bit more as it takes more fuel to make HP, but you'll save a bit cause your rig, when going up a lot of grades, will now drop into 4th gear, instead of the "screaming 3rd" gear which causes revs to go way up.
Besides, if your that worried about a tenth or two less gas milage per gallon, well then, get a Prius and buy a tent.
Those of you who are skeptical...nothing will change your mind, and you can argue against it all day long.
Then there are those of us who have it, love it, and wouldn't be without it.