7.3 Powerstoke help

I have an Excursion as a tow rig which i love to death. Im looking to see what mods can be done boost my mpg. I drove to Austin to Houston and back last weekend without towing anything and averaged 15.77mpg at 347 miles - hand calculated. 95% of that was highway at 65-75mph. Im asking about this is b/c im somewhat jealous of my buddies 2500 Dodge getting 23mpg to Austin to Dallas and back.

Thanks in advance.