For a while I have run 75W90 Severe Gear in my 88 4Runner with Detroit TrueTracs in front and back. These are non-clutch limited slip diffs. I'm looking at freshening up the gear oil and am considering going with Amsoil's cheapest 80W90 synthetic lube to save some $$.
My question is, what is the added value from this cheaper grade to the Severe Gear grades? For low-HP, around-town and occasional moderate off-road use, is the more expensive product that much of an upgrade?
I still want to stick with Amsoil as I believe they do a great job with their drivetrain lubes. I run their MTF in my Hondas and MTG in the 4Runner and have always been more than happy with them.