Like stated by cmdr jim, your best bet is to get an entire front differential from a junk yard that already has 3.73 gears installed. That makes the swap so much easier and costs a lot less. All you have to do is drop the front diff and swap in the new one. As for the rear my buddy Jay purchased 3.73 motive gear ring and pinion for a chrysler 8.25 rear end. After everything is installed, purchase the Hypertech Speedometer Calibrator and change the gear ratio from 3.07 to 3.73's and enjoy! The Hypertech Speedometer Calibrator is upgradable to the max pro so you can tune your 3.7 liter at the same time. Jays 3.7 Liter WK has been rolling around with 3.73s with ablsolutely no issues what so ever and his gas mileage has even increased. He has a 4 inch BDS lift with 33x12.5R18 Toyo Open Country MT's.