Ned: I'm not doubting your tests and in fact was eagerly awaiting some feedback.
The open differentials have never been a problem. The spider and side gears will take a beating and keep on ticking... but who wants an open differential?
The way I see it (I may be wrong, perhaps someone at Visteon can clear things up?) the Traction-Lok in the 7.5/8.8/Dana 60 works like an open differential with the exception the clutch/steel packs allow for limited slippage so that one wheel can turn faster than the other in a turn. So, in an autocross situation/city driving (or NJ city driving - btw, there are almost no straight roads in the NJ suburbs, everything is twisty/turny unlike SE MI which is a big grid) the clutches are slipping each time you make a turn.
I've been told that clutch slippage in a tranny (Torque Converter as well) will build up heat and ultimately just break down over time unless you keep changing the fluid. This is where the shudder issue comes to play w/ the 4R70W...
I do not have empirical evidence, but was told the Torsen differentials are even harder on the gear oil. They supposedly build up a lot of heat from the pinion/side gear meshing (i.e. a 3 pinion prototype offered by Tractech tested by Bob Cosby will have 6 pinion gears and 2 side gears meshing together like one big rotating orgy of metal and oil) and can shear out the oil very quickly. This is just from regular driving (making a turn, etc...)
As-is, my 8.8 takes about 2.25 qt of oil. gdmjoe said he got an extra 1/2 qt from the SVO cover so that puts us 1/4 qt shy of 3 qt which is still better than what we have before.
If the carrier bearings were roasting, that can change the backlash and pinion/ring gear meshing as well as bearing preload. Not to mention that on a Traction-Lok differential, the clutches will die an earlier death. Ford must use a lot of FM additive from the factory and/or improper preload to allow much more slippage (to cut down on the # of complaints)???
Wes said he never got more than 5k out of his factory Traction-Lok installs. I've heard more than one Marauder owner complain they never got more than 20k miles.
I drove the E-250 with the Dana-60 + Traction-Lok and I don't know for sure, but I can hear something slipping when making turns and it is not the tire(s).
I've never heard the left rear wheel spin and once when it got stuck in our drainage ditch (I was not involved! My dad was driving it), the left wheel was sitting on solid pavement w/o so much as spinning to help bring the vehicle out. My guess is the Traction-Lok was toast at 12k miles. I had changed out the gear oil at 500 miles to Redline 80W-140 (Ford calls for SAE 90 dino + 8 oz of FM). Either Redline adds too much FM or the clutch preload was set too loose or the clutches just burned out (3 qt capacity though). It's a low speed vehicle (limited at 89 mph).