I'm going to change the fluid in the rear differential on my 2009 Dodge Ram 1500 4x4. The recommended weight is 75/140 which is what I will use. I plan on using a full synthetic, and just wondering if anybody has a recommendation as far as brand. Rear differential fluid is something I know very little about, but the rear diffs on Rams can be a problem and I'm trying to improve the odds by using the best possible lubricant. Greatly appreciate any comments.