Yeah never touched. 50K isn't late or anything. Maybe a little late if you have a rear LSD (05-09 Sports and some SR5s).
I usually do my diff fluids and transfer case every 30K miles.
3.73 gear with LSD '06 SR5 has the sticker. Rearend is quiet though. I bought it at 47k in Jan this year.
Specs for fill from my owners manual are:
trans 1.9 quarts SAE GL4 or 5 75W-90
transfer 1.1 quarts SAE GL5 75W-90
front diff 1.6 quarts SAE GL5 below 0 degrees 75W-90
rear diff 3.0 quarts SAE GL5 below 0 degrees 80W or 80W-90 above 0 90W
also add LSD additive for LSD rear.
I'm also doing the rear breather mod.
Have all the stuff now to do everything. That is if it would quit raining.
My Hayes manual says the same except front gets 80W-90 same as rear.
Using Royal Purple 75W-90 in trans & transfer case and Valvoline Durablend 80W-90 in front & rear
that will give me about 2% LSD additive at 3 quarts so will add a little additive to it to bring it up some if it chirps.