Are we talking about the Z-F, 4-speed AOD? If so it is the very same transmission that came in 'S' class M-B, 6-7 series BMW and all big Ford cars. I know of at least a dozen of these units in big M-B's (380 lbft and 5000 lb vehicle weight) that have well over 400,000 miles with ZERO problems...of course M-B says you should change fluid every 2 years or 25,000 miles and Ford says you should NEVER need to service the same transmission but then again the Ford unit is good for only about 125,000 miles.
I think you'll be good to go with the AOD...plus you get a shorter 1st and something like 30% o.d.