Anyone tow with a Ford E350 van?

Am helping a friend of mine look for a new tow vehicle for boat pulling duties. We were discussing how convenient the E350 vans are and were wondering how well one would pull a boat (he has a 2009 X star). It looks like most of them are equipped with the 5.4 liter V8 engine and 3.73 gearing, which I have heard are weak, but have no experience driving one myself. They are available with the V10 and 4.10 gearing which I am guessing will be better, but harder to find.

Anyone have experience pulling their boat with an E350? What drive train did it have and how well did it tow? If you don't have experience with the van what about the 5.4 engine (in the truck or something else) pulling a boat?