I agree with John Browning on the differential fluid. Redline is great stuff. I tend to use Mobil 1 whenever possible, be it engine oil, ATF or gear oil. However, my '03 Tundra limited slip rear end calls for straight 90 wt., and Mobil 1 makes either 75W90 or 75/140...and the 90 is a thin 90 @ 212F. So, I checked the specs of the other synthetic fluids, and, as John discovered, the excellent Tinken load and good, strong 90 wt. at 212F sold me on Royal Purple 75W-90. I DO use Mobil 1 in the front diff. & transfer case, as Toyota calls for 75W-90 for both. My 2003 was built in 11/02 and it calls for T-IV ATF, so that's what I use. John's Mom's '03 must have been one of the really early '03's to call for Dexron. I believe the Tacoma mentioned in the original post is almost certainly spec'd for T-IV.