5.3 & 4l60e gearing ???

[rs72z]

I thought i would ask this even though i feel i know the answer.

My cc dually has a 5.3 & 4l60e in it with 4.10 gears. The first tank i checked it got 17 mpg. I dont have a tach on the truck so i hooked up the Modis to it to check the rpm's at 70 mph. It's turning right at 2300 rpm at 70. most late model trucks are in the 1850 rpm range at 70.

What i am wondering is, if i went to higher gears would the weight and areodynamics of the truck cause it to work harder and not allow any better milage?
Lets hear everyones thoughts on this.