4R100 trans. Gear ratio you would have to give us the code on the door. Or remove the diff cover and read the stamp on the ring gear. It is there trust me on that. Only problem is you would have to change your diff fluid at this time as well. Or you can mark the driveshaft, mark the tires. Put the rear on jackstands. Chock block the front tires so the truck won't roll, put the trans in nuetral and spin the tires. Count how many revolutions the driveshaft makes for 1 revolution for the tire. This will give you a pretty good idea on what gear ratio you have.