Can someone recommend a really good oil for the front and rear limited slip diff and also for the transfer case on my Ram 1500? 75w-140 rear 75w-90 front. Transfer case (NV243) calls for atf+4. Looking, or should I say, dreaming for something that might show some efficiency gains in mpg. My common sense says to wish in one hand and [censored] in the other and see which one fills up faster LOL My initial thoughts were Royal Purple, but I am open to suggestions.