Found two near identical equipped trucks on the lot and spent some time comparing. Both fresh builds. 145" wheelbase, 4x4, 5.0, tow package, 36 gal tank, 7,000lb GVWR package. One had the 3.55 elock an one had the 3.73 elock. The 3.55 had an 8.8" and the 3.73 had the 9.75" diff. Odd thing is both trucks had identical 3,800lb RAWR. Anyone who knows these two diffs knows the 9.75 is much more substantial, but they had the same spring stack and same weight rating on these two trucks. The 3.55 equipped truck tow rating was 9,100 and the 3.73 was 10,900. Both had the same 11,600 sticker on the hitch.

Just and FYI. Get the 3.73 and without a doubt you get a stouter diff, but it will have the same RAWR on a 5.0 equipped 145" truck. No matter to me because I'll be adding air bags and exceeding RAWR, so I'll be doing it with the 9.75".

 

Adding air bags doesn't allow you to exceed the RAWR. If you need increased payload capacity you may want to look at a Super Duty.

 

Didn't ask permission, said what I intend to do. Feel free to write me a ticket when you see me on the highway.

 

The reason is pretty simple... higher numerical gears = SMALLER teeth on the gears. So if you go 3.73 in an 8" diff, your gears are going to be a lot smaller than 3.73's in a 9.75. I assume that to maintain the ratings, they needed to go to a 9.75, else have gears that are too weak.

 

My Ford Motorsport race 8.8 diff came with 3.73. The 8.8s I have seen fail fractured the housing. Not on a truck though.

 

 

Same.