OK, I know I'm stating the obvious to many here, but presuming you've kept up on all TSBs/Recalls, but your butt dyno is telling you that your '8 is just not as peppy as it should be - change your sparkplugs!

Mine had been dealer-replaced at around 12k miles as part of the voluntary emissions recall. Now at 20k and prepping for the season I changed my 'plugs myself and it's made a noticeable difference. They weren't really too bad to look at; some brown/black ash/gumming, but definitely time for a change. Going forward I'll change them out much more regularly.

I went with stock OEM plugs from FluidMotorsports (very good price and excellent service).

Of course air/oil filters and all fluids regular changes are also important, but "don't underestimate the power of Force" of the sparkplugs!