There are a whole range of power chips and upgrades.. The two best are.. Banks (Of course) and UltraPower.. Now with Banks, I do not think there is a hope in heaven of recovering the cost of the upgrade, The slight MPG increase you MIGHT get will never pay for the system..
With UltraPower.. It is possible.. In both cases the systems have been tested on the 8.1 and though I have never heard complaints about Banks.. I have heard the praises of both Redlands and Brazil's (UltraPower dealers) sung all over the forums. I myself will most likely to to Brazil's when the time comes. These companies stand behind their work.
On the other hand I've heard of fly-by-night upgrade outfits who ... Well, often as not you wind up with serious after-upgrade problems.. Like blown engines and non-working brake systems and stuff like that.
Home is where I park it!