My 2010 6.4 had a limited slip axle and it wasn't worth a crap.

The limited slip axles in the Ford's is not an auto-locker. The truck I had before my 2010 was a 2003 half ton chevy and it had an auto locker in it. That worked quite well. In contrast, the limited slip in my 2010 ford was worthless.

The way the limited slip axles work is there is a clutch pack inside the diff. The clutch offers resistance to the axle shafts turning against each other, like a brake on a wheel - it doesn't lock the axle up it just resists it moving. This transmits SOME of the drive power back over to the wheel that has traction in a limited traction scenario, not all of it as a locked axle does.

That having been said, the SRW trucks have traction control (not sure about the DRW's? Is it just stability control they lack?). The traction control on my truck works well enough that I can't hardly get the tires to chirp if I stomp on it. Once the turbo kicks in the tires will spin briefly then the power is dropped and all and the tires stick. I have not tested this theory yet, but what someone explained to me a while ago is that the traction control will control the individual wheel brakes. This tells me that if one tire is spinning the traction control will brake it. On an open diff if you brake the wheel spinning that power is sent to the other side of the diff - the wheel with traction. In essence, it does the same thing as a limited slip - clutch pack in the diff = brake pads/rotor on the spinning wheel.

My opinion - the ELD is the way to go. My limited slip diff in my 2010 was so bad I had to put the truck in 4x4. With the ELD I turn it on and away I go - most of the time For the other times theres 4x4.