I have a 2001 Grand Prix GT and I've noticed over the past few weeks that if I drive at 60 MPH and either just keep it there with my foot or cruise control my gas mileage is 29-30 and the RPMs are steady at 2000 however once I hit 65 or over I lose 5-6 MPG and it drops down to 24-ish and when I first bought it the gas gauge didn't drop nearly that fast when doing 65-70. Are there any common gas mileage problems with the Grand Prix's?
I know that there is a minor coolant leak in the throttle body/upper intake and it comes out a little bit when you really punch it as well as the top right seam on the radiator is hissing which will be getting fixed soon but the car has never overheated, or gotten any hotter according to the temp gauge unless it sits running in hot weather on the freeway in traffic. The transmission has been replaced with a TripleEdgePerformance one when the original one went bad and seafoam has been used as well.
