On my last few runs i have been trying out
Ofna Diff Lock Lube in the Slipperential. Contrary to my expectations there is a fairly discernible difference compared to running 500K. The truck feels different when turning though it's hard to describe how and it really does feel more locked up 4WD wise. I think it would be hard to tell the difference between this and a locked diff. I prefer this though as there is still some give in the center diff to help dissipate end to end drive train shock. You can still turn the diff by hand albeit very slowly and requires more force than the 500K.
Also filled up the Vorza\Hot Bodies diff with the Ofna Diff Lock Lube and it was a bit harder to turn than the Slipperential, not sure why, maybe its just a tighter diff. For a CD with more gears like Jahay's spider, 500K may be all that's need for a really good locked up feel.
I'm giving up on the stock tires for good. They just don't have the grip an XL length chassis needs to get the power to the ground. I threw on some old HPI GT S tires after driving on stock for months and the difference was amazing. The truck instantly felt like more of an animal, much more fun to drive.