Still geting 27mpg highway, car has bolt ons now headers, 90mm LS6 intake, Strano sway bars, springs & Koni's, Hawks sinister LCA's & panhard, EBC brake upgrade, Hotchkiss strut tower brace plus SS hood & spolier. Had 10 bolt w/3.73's installed last week plus aluminum driveshaft, that's probably the end of the 27 mpg.