You can get 3.55, 3.73 or 4.30. The 4.30 gets a heavier duty rear end(Dana M245 has larger ring gear, 10.8", larger axle shafts, 4" tubes) vs. Sterling 10.5(3.5" tubes, smaller axle shafts, 10.5" ring gear). From what I can gather average MPG only drops by 1 and everybody recommends the 4.30's...