My Z spec T5 whined at high speeds the day I put it in. At first, I knew it was a little low on oil, but I soon topped it off and while the whine wasn't as strong, it's deffinately still there. What's in there is about 2 quarts of Valvoline mercron/dexron III ATF, and 1/2 qt. of Castrol merc/dex ATF. Both non-synthetic. Several people have told me to try red line synthetic atf. On the summit website, they have: Dexron II/Mercon, Dexron III/Mercon, and synthetic racing fluid. Which one should I get? What's the difference? Would it help with the whining?