Are you serious? I need to definitely look into this then. I just got 14.3 mpg on the last tank and that is good.
With gas priced at $3.75 card price I need every mpg i can get.
He most likely has a different gear ratio in his rearend than you do.
If I had to guess he probably has a 3.42 or 3.08 and you may have a 3.73 like me.
Of course mine is a 08 Suburban so I have the 4 speed transmission as well but mine with cruise set at 73 MPH turns about 2000-2100 RPM and netted about 17.5 MPG on my last interstate trip.
My truck has a K&N filter and Air raid MIT and a free flowing muffler and has a custom Diablew tune via the Diablo sport I2. Just for reference.
Also I average around 15 MPG in town.