According to this document which tells you everything you could want to know about 17" TRD RW fitment on Tundras, Sequoias and LCs, Toyota recommends 46 PSI in LT285/70/17s on a LC.... LINK
I just tried 46 psi from 38 psi and ride is much nicer on my RW/KO2 DT (Different Tread) tires. I'm going to try 56 psi to see if there is a further improvement. My back doesn't feel like a slinky anymore at 46 psi.