[sierrap615]

got this off a webside that sells a few red line fluids, but in short, its synthetic and designed for racing.

The D4 ATF is designed to satisfy the improved low-temperature requirements of the new Dexron IV specification, and the improved shear-stability requirements of the new Mercon specifications. The D4 ATF also provides significantly improved gear protection and will provide a GL-4 level of gear protection, making it a superior product for transmissions and transaxles. The balanced frictional characteristics provide smooth and consistent shifts for extended drain intervals. The superior stability compared to petroleum ATFs allows high-temperature operation without varnishing valves and clutches.