I think you should plan on using closer to the 12 quarts of trans fluid as recommended by the FAQ. I've just last week finished three AW70 flushes and, give or take, that's what it took to get reasonably clean fluid out the return lines. I probably could have used even more if I was a purist as two of the three cars were obviously overdue based on the initial outpouring.

I can't speak to Sea Foam TransTune. With or without an additive/cleaner you're going to want to do a thorough flush and will need the same amount of fluid. Many will spout the virtues of synthetic, but honestly, unless you're towing or otherwise overheating the trans, then I'd save the money and do the flushes more frequently. It's really no more difficult than doing an oil change once you've got the cheap little funnel, a length of vinyl tubing and spend a few minutes calibrating milk jugs.

While you're under the car, if there's any sign of weeping around the trans pan gasket then snug up the bolts (snug, not over-tightened). I was amazed at how loose a few of them were.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now