Do any of the gearboxes come with synthetic gear lube? I live in a cold climate and would like to switch to synthetic if it's not in already. I'm refering to both diffs, transmission, and transfer case. I did a search on transmission lube and see there's been quite a few heated discussions on the particular brand that should be used. I have 22,000 light duty miles on it so my objective is two fold..... change just to get fresh oil in there and second to gain the benefits of synthetic. Is 22,000 miles too soon to change?