I have a 98, 4.0 w/ abt 160K miles. I get similar milage in the winter with the hardtop, full doors and a back seat. In the summer with soft doors, a bikini top and no back seat, I get 18-20. On the highway, 18k to 22k rpms, no warm up or leaving it at idle to keep the cab warm. Details can have an impact on milage... fully inflated street tires, a weight loss program, synthetic oil and a light foot all help. No one factor makes a huge difference, but added together there can be some improvements.