Two seperate, but possibly related, issues.
1) My gas mileage has gone down lately, from around 22 MPG to 17 . I use Sunoco 91 octane, keep the tires at 35 PSI (Goodyear Regatta 2's), and use 10w-30 motor oil. I usually drive 70 - 80 mph on the highway with the cruise on (I do have a heavy...