Well, thanks to all for the info, but I guess I'll take Chocdante's as the "flavor" of the truth I'd like to hear.
Larry's right, I probably drive it a little harder than last year, but not that much and not nearly as hard as my BMW's.
I can attest that last year I did get 27-28 on the highway (in the mountains over the continental divide) and on general trips up and down the front range.
I guess I'd still suspect a possible O2 sensor problem.
Thanks again everyone.