Had to replace my Accord V6 tranny for the same reason, luckily it was under warranty. They said it would have cost $4,000 otherwise.
You have to change the transmission fluid on these transmissions VERY frequently. Like every 15,000 miles, maybe less. It will already be dark and ready to change at that point. My manual recommends 120,000 miles between changing fluid, which is an absolute joke since the transmissions won't even last that long if you don't change the fluid.
The problem was that these transmissions are essentially five individual manual transmissions with their own clutches, and to smooth out the gearchanges, the clutches do a lot of slipping. They build up heat very quickly and toast their fluid. It was an overly complicated design, IMO. The Honda Accord service manual has over 300 pages devoted to nothing but the automatic transmission on the V6 model!
After you get your transmission replaced, I have found that changing the transmission fluid is actually pretty easy to do yourself. It's not really any harder than an oil change once you find the fill and drain bolts and get the right tools (I needed a couple socket extensions and a fluid pump to reach the fill hole in the engine bay). Honda's ATF fluid and appropriate crush washers for the drain and fill bolts can be found cheap at handa-accessories.com (yes, hAnda, not hOnda). There isn't a consumer-serviceable filter, so you don't need to worry about that.
Good luck. 🙁
