i have a superchips and it gives me a noticeable improvement, not in mileage though, i get crap mileage on all my vehicles, must be the leadfoot and my ethanol filled gas.
fyi custom tunes, unless its on a dyno, will still be a form of a canned tune one way or another. they take your current programing strategy code you provide, and just pull up a canned tune for it, and maybe tweak it just a bit depending on how the tuner normally likes to do it.
dyno tune, or everything else is canned, i am happy with my superchips tune btw.