I have an 05 TB 4.2I w/42,000 miles on it. Commuting on a daily basis on back roads no faster than 50 mph I get an average of 18 mpg witch I thought was pretty good. This past weekend I took a road trip to up-state NY. All Highway, 65 mph+ the whole time and I only averaged around 19+ mpg. Is this normal? I thought these would get at least 20+. Heck my 02 Silverado w/4.8L V8 gets 20+ easy. Any suggestions or should I just be happy w/ the 19+ ????