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The Red Line MTL 75w80 works well, BG SynchroShift II works well too, Motorcraft XT-11 QDC has been the best for cold feel for me but is super expensive if you are tracking the car.XL-18 additive made a difference too if you can still find it.
I've used BG fluid ever since first fluid change. It is a little notchy in freezing temperatures, but it gets smooth after a couple of shifts.
I had the transmission opened up at 28k, thinking I had messed up the synchros after shifting issues on track (turned out to be a failed stock clutch). And the mechanic told me the gears looked like new, even with my non-rev matched downshifts at the track. So go up to the 75w-80 if you want better gear protection, and don't mind to compromise some smoothness at cold temperatures.
I used to replace the fluid annually, but after hearing how hot the transmission gets, I may replace the fluid after 2-3 events.
I agree with everything above. I have run the MTL and the QDC. The QDC is the best cold shifting fluid, but if you are tracking the car I would use the BG or Redline fluids. They will provide a little better hot protection and are half the cost making frequent fluid changes much more reasonable.
I wouldn't look for a fluid based on how well it shifts when cold if you are looking for something that can stand up to track abuse. I can't really say the thicker the better but the thicker the better. With how hot the transmission gets on track you will have better protection with something a little thicker. I use Royal Purple MTL and my transmission has 14,000 miles on it, most of which are track miles, still on the stock clutch too. The Ford stuff made it shift better when cold but won't offer the protection on track you are looking for.
I agree with everything posted and have used all but the BG. If you're still under warranty, 5yr or 60,000 mile on the trans, I'd stick with the Motorcraft XT-11 QDC for warranty reasons. There have been enough failures that I'd be worried about your trans not making it to the end of the warranty period.