Thanks for the help. I do run a lot of AE black grease in the thrust bearing, but not on the spring, I should try that. I was running the older (?) style of diff screw with the threads all the way to the top (and it broke), and have now switched to the other style. As to the diff tightness, I had thought I saw that Chris Tosolini ran the diffs on foams: full tightness on the front, and one-quarter loosened on the rear, and this is where I was running them. From now on I'll run them a bit more loose than this and see how it goes.
Any advice on proper diff break-in? Do people just run diffs to break them in or do anything else?