I installed two years ago Redline Heavy Shockproof to my H3 front and rear differentials...
Redline Heavy shockproof is something like a 75w90 but with a film protection of a 75w250 or something like that
I has problems with my front differential after putting a Outfitter Design three poly bushing mounts, because my ring and pinion seems warped and cause noise....well after trying a lot of different friction modifyers and additives, I put the Redline and reduces the noise like a 90%...awesome!
I recently add to both differential some additive to reduce friction...but not necessary because I dont notice any differences..
So...my recomendation is to go with Redline Heavy Shockproof