You'll be fine. I have been using the Amsoil severe gear 75w/90 in my '03 V8 4x4 Limited, full time 4wd as well, for over 100k miles and no issues whatsoever. I put it in about 145k when I purchased it, and changed it at 230k and the fluid was still in great shape. Only did mild 4wd trails and probably about 5k miles of towing around 4000lbs. Low temps pushing -30 in the winter when I lived in the ID mountains, and +105 summer temps in Boise. I'm about to hit 250k and it still runs as good as new.
Also I have been using the Amsoil signature multi-vehicle ATF the entire time as well, no issues and perfect shifts. Mine has a trans dipstick as uses T-IV fluid, not WS.
Last edited by toytaco970; 06/29/20 05:38 PM.