I got the original AC Delco plugs installed today replacing some bosch ones and the milage is allready way better.
I got allready 21 miles/G instead of 17. That´* a big difference. I ordered the O2 Sensor so i should be able 2 intall it next week to see the difference. I only had the car now for 5 days but i try 2 do my best. But the car is amazing. It´* just the best combination of power and luxury. I just have 2 delate all the little problems.

I got 34 mpg on a trip to new mexico this summer....70-75 mph.....

Michigan Winter air gave me the best milage.... Magic 40.

My mpg is horrible, I am getting like 15 mpg city, and 21 mpg highway. I have changed my plugs and my PCV valve. I have 1 step colder plugs. As well as some mods, but would that lower my mpg that much? Tire pressure is fine. I am thinking of switching back to my stock airbox, to see if its my open cone. The only other thing I can think of are the fuel filter, and O2 sensors.

Yeah, I think Seth, you, Seth'* friend (forgot his name) and me were grinning from ear-to-ear when two Bonneville'* pulled 40+ so it definitely wasn't a fluke.

are your plugs made by Bosch too by any chance??? If they are, they need to be replaced by some ACDelcos.