Well what else can I do to help my MPGs in my GT?
Since I've got it, I've replaced the engine of course. But I have new fuel filter, fairly new plugs (they were used for a month in the 3800 that spun a bearing) with about 2000 miles on it, new air filter, and 34 PSI in the tires for the cold weather we have right now.

The only factor I can see hurting my mpgs is the PO420 that came on a couple days ago.
I get about 17.7 though on average. It can be better now, I don't drive like a mad man...all the time.