I have 2004 4Runner with the 2WD / Full Time 4WD / 4 Lo transfer case. I need to change front & rear diff & transfer case fluids. The manual calls for: Front diff: 75w-90 GL-5 Rear diff: 90w GL-5, or 80w-90 GL-5 below -18C / 0F Transfer Case: 75w-90 GL-5 Both front and rear diffs are open, no limited slip. Typical temperatures in my area range from approx -30C / -20F to +30C / 90F. I'm considering Amsoil Long Life Synthetic Gear Lube 75w-90 in all 3. I can get it off the shelf at a store in my area and a little cheaper than Pennzoil Full Synthetic GL-5 or Castrol Syntec GL-5. I know Amsoil Severe Gear is also good but more $ and not as easily sourced. It also has limited slip additives which I don't need, although wouldn't hurt. Any thoughts on Amsoil Gear Lube and using 75w-90 instead of 80w-90 in rear diff?