TSS/OSS is definitely a viable suspect, especially if the flares are harsh. But to be sure, I would send a fluid sample off to Blackstone labs for analysis. If that turns out fine, then I would think about replacing these and possibly the valve body (at least cleaning it out).
I have found that the MAF sensor on my Edge can also contribute to the problem because it feeds into TCM shift logic. I tried cleaning time after time, did not help. Putting in a new one made a big difference. So maybe you can try cleaning/replacing the MAP sensors. Also check the throttle body, because the motor sometimes fails.
Other than that, there are TSBs for bumps/harsh shifts that you may want to look through, but since the problem seems to be progressing, I am definitely thinking TSS/OSS.