IIRC, E40D remains the weak link, although I also recall that there are companies able to correct the OE shortfalls of this tranny. Ferd's van configurations tend to make the engine bay more challenging for maintenance.
The E-350 and 2500 Burb are probably about equal for hauling. Rear gearing and engine sizes come into play for each platform. Do admit that I have not gone Internet diving to find the owner's manuals of each item and am going from memory.