Scott, FWIW, My Wifes 04 Yukon(2wd,5.3Z,3.73 axle,115K) was purchased new and has from day 1 gotten 15-16 around town and 16-18 on freeway @65-75mph. I have to say I am guilty of not always buying top tier fuel and only use 87 which around here is 10-15 ethan... Login to read more.