Have you guys ever tried RCSpeedworks diff grease? Very very sticky and heat-resistant. I have been using this the last weeks now and it is far better than Schumacher grease. I've tried everything from Associated, Schumacher, Trinity, Serpent and so on, but the RCSpeedworks grease works the very best for modified (or anything else). No more slipping diffs for me and almost maintenance free racing.
Also tested and occasionally used by Jilles. You just need a small amount and you're ready to go.
Nothing else for me.