60mph w/ac off Will get you 25mpg I get much worse as soon as AC goes on. Amzoil 5-20. Or They just came out with a 0-20 extended drain intervail. I've been using Amzoil for 25 years and swear by it being the best oil out there.

 

I have headers also and My HWY mileage has not be effected. I run 23-24 on the hwy.

14 around town and that is floor boarding it. ha!

 

The car is back and good as new, The gas mileage is a bit off though...