I like Lubro Moly syn. GL-5 hypoid 75w90, used it front, rear, and in the t-case this time around mostly becuase the bottles come with very handy spouts that make filling the diffs/t-case much easier. I've used it for years in my Mercedes and F350 Powerstroke truck, it's a little more spendy than M1 but it's never done me wrong.
I did a complete fluid change on my parent's 02 Tundra TRD this summer and did some reading that the rear LSD on that rig doesn't like synthetic much, so I used Castrol Hypoy C 75w90 and some LSD additive, all seems well even after a 1500 mile trip in the summer to the So. Cal desert in temps of over 115f.