I don't understand why I get the same MPG

It does not matter if I am towing my utility trailer with, or without my 4 wheeler on it(which weights less then 1k total) my 18 foot bass boat (which weights little over 3.5K, including the trailer) or a bob cat on a equipment trailer ( weights over 6k) I end up with around 11 mpg. I the 4.6L v8. not that I am complaining, I am just trying to figure out the science behind this.

 

I am using 2 different methods. 1- I fill the truck up and reset the mph avg. tracker in the truck. 2- I use the file tracker app., that shows you your best mpg, your ave., and your last mpg. Since I my hunting club, the lake and the property I Ben using the equipment are all over an hour away. I fill up the truck before I hit the road and when I get back home.

 

Try the old fashioned way.