I have an 04 6.0L Exc. w/30K miles and no trans problems at all. There was a recall on the trans, I think something to to with a planetary gear problem. Brought it in, they changed it, changed trans oil and filter. I had some engine problems early in it's life (around 3k) but I have a really good mechanic here in Orange County and running great now. I heard the problem transmissions were with the pre 6.0L trucks/Excusions (pre 03) with the 7.3 engines.
You could post your transmission question in the "PowerStroke Engine and Drivetrain" section if you haven't already. Same trans in the trucks I believe, if I'm wrong someone please tell me so.
Good luck, and let us know what you end up buying.
I almost forgot, welcome to the forum, alot of really good info here!