hey everybody...
i have a 99 250sd, 5.4 with 3.73 gears...i want to get a set of 4.10 or 4.30...i have read other threads..but havent found my answer. is switching out the gears going to make that much of a difference (gas milage and seat of pants power). also what is the difference with non-limited slip and limited slip, is non posi? im looking to go to the junk yard and get a complete rear and front, but im not sure what to do yet...thanks..

 

You'll probably get better mileage with the 4.10's then you are getting right now. The 5.4 is definitely small for that truck and the extra gearing will help it stay in a more useable power range. 4.30's will definitely give you a better "seat of the pants" and towing experience. You'll never offset the cost of the parts with the gas mileage you may or may not get though, so you may as well toss that out the window.

Non-LS, or open diff, allows one whell to spin free in slick conditions. LS helps control this by using a clutch, cone, or gear setup to apply torque to the wheel with traction. It doesn't lock, but it limits how much free spin will occur. LS is well worth it.

IF, notice IF, you can get the items at a salvage yard. Look at between 600 and 1,100 dollars to install, unless you are gonna do it yourself. If you buy new gears, master install kits, and an LS you are looking at almost a 2K expense, including the install, for a 4x4.