If you're even thinking about 35's then just go to 35's. Re-gearing is not a must but you will want to do it at some point. Gas mileage is going to suck no matter what, you dropped 2mpg's just by thinking about 35in tires.
11 JKUR Auto, RIPP SC, Body Armor bumper, Warn XD9000I winch, Synthetic line,XRC Rear Bumper W/carrier, OBA W/1Gal Tank, 10lb CO2, Metalcloak 3.5 springs, Synergy track bar,drag link flip-Tie Rod, control arms and Ball Joints, C-gusset and sleeved, RuffStuff Diff. covers, FOX W\res shocks, Barricade Flat Fenders, 37 12.50\17 BFG KO2, 5.38 Motive gears, Uniden 520xl CB, Yaesu FT7900, Teraflex Big Rotors, Diablo Intune, Dynomax RC exhaust Redneck Ram. W3JEP San Diego Jeep Club-Gulf War Vet. USAF