Dexron is the most over-engineered fluid in your car. I'd replace the air in my tires with pure nitrogen before I'd worry about switching to synthetic ATF, which can never return more than a fraction of the benefits that can be gained by switching to a synthetic engine oil (which is subjected to combustion byproducts and excessive temperatures, and also expected to remain as slippery as possible).

For most applications, synthetic ATF is a total waste of money, though it might be good for your peace of mind iff you regularly use your passenger car to do a lot of heavy trailer towing in hilly terrain in high heat under stop-and-go conditions.

I let my AT flush it's own Dexron ATF (with more of the same) at 61K miles after much heavy use. That's the only maintenance it's had, and it's still going strong. I owe the car a timing belt; I may do the flush ritual again at that time for the hell of it.

I am wary of "flush machines" (nevermind their chemical treatments!), and consider draining/refilling to be worse than no maintenance at all.

After suddenly switching the fluid from well-used to new, its "grabbiness" factor will suddenly change. Rather than have the AT figure this out from new experiences, better to pull the AT's ECU's fuse for a while and then have the AT start out in learning mode with the new fluid.

My hunch is that most of the horror stories you've heard are not only broadcast way out of proportion to the happy stores that were never told, but involved cases in which there was already a transmission malfunction that had chewed up the old ATF, so, unsurprisingly, flushing the ATF did not help the situation, any more than a blood transfusion can cure someone who's suffering from leukemia.

- Dave; '95 854T, 143K mi