I have never towed with mine but I didn't notice much of a drop in gas milage or power with the 30x950s but I did add a K&N open filter and a 2 1/4" exhahst with a MagnaFlow. When I went to the 31s I felt a drop in both milage and power but not enough to make me go smaller tires again. A good air filter and open up your exhaust and It should pull ok with the 235s.
Dennis

95 Sportage, gone but not forgotten.
98 Jeep TJ, 4" Zone springs with RC Long arms, Ford 8.8", 4.56 gears & Detroit locker rear, D30, 4.56 & Detroit Trutrack front.