I CAN TELL YOU GUYS FOR A FACT EXACTLY WHAT HIGHWAY MPG CHANGES FROM 3.31'S-3.73'S LESS THEN 2MPG.. I can tell you this for sure because i just drove the car back from california to NY last week.. I averaged 22.5mpg's at 75+ mph the whole trip (2700 miles) and I used to get 24 mpgs w/ the stock 3.31's on all my 500+ miles trips.. and after i fill up the 1st tank of gas and head on a long trip, I reset the avg mpg and dont reset it again till i get home, so these are real world, including stopping to eat, re-fill on gas, traffic, etc... And I can also tell you that going from 3.31's - 3.73's it turned my car from great looking to GREAT FUN!!