Hey guys, for the past few months I've been eye balling some good 75w-90 synthetic gear oil for the differentials and T-case on my Tacoma when it hits 15k, get all the factory fill stuff out (dino 90wt). Well it's quickly approaching. I've been eying the M1 and Syn power. I have used the M1 in prior vehicle diffs with no issues. I've never used Synpower, but plenty of Durablend 80/90 also with no issues. Looking at the M1 vs Synpower PDS's the only difference is the Flash point and Visc. The M1 has a slightly higher Flash point and the Syn power has slightly lower Visc cold and warm. I also noticed the Synpower carries the Mack GO-J approval and the M1 does not (for whatever reason, maybe they didn't see the need to apply for it). Between the lower Visc and Mack approval I'm leaning toward the Synpower. but it is more expensive $11 vs 9/qt (adds up when you need to buy 8 bottles!). Is the slightly lower visc going to yield any better MPG's? Is the extra $ worth the Mack GO-J approval?