I have a 94 Jeep Cherokee that was getting 25 miles to a gallon but is now getting 18 miles to the gallon. I tuned it up and changed the o2 sensor but it didn't help. The car is a 6 cyclinder standard transmission and runs extremely well. My daughter had it for 3 years and I guess she never checked the mileage. I use fuel supplement every other tank of gas. Any suggestions appreciated.