More Miles per gallon

I bought a 2008 Jeep Liberty in January 2015 with 42,000 miles on it. I travel 2 to 4 thousand miles a month. I have only been getting 14 to 20 mpg. I finally added Additech cleaner and I no longer have rough idle and I'm at 17.3 to 26.2 mpg. What a total change. Thank you

Melissa

Belton State, Texas