Mickey,
Your tires are not fighting one another. They’re just consuming fuel at different rates.
Your front tires are likely getting better fuel economy than the rears because they are more worn and have the worse treadwear rating. Replacing those with a pair of tires identical to the rears is only going to make the fuel economy situation worse, and it just might be, you’ll never get the fuel economy you once had.
It’s those long trips that really emphasize the difference in RR of tires, since most of the fuel is consumed by either aerodynamic drag, and driveline inefficiencies (tires being part of that!).