As mentioned above, the E350 v10 or diesel can tow more than 10,000 pounds with an aftermarket hitch. The published tow rating is limited by the factory hitch and not GCWR like most vehicles.
E-series GCWRs
V10/3.73 = 15,000
Diesel/3.55 = 16,000
V10/4.10 = 18,500
Diesel/4.10 = 20,000
V10/4.56 = 22,000
I've towed over 200,000 miles with my v10 and I'm coming up on 420,000 overall. Typical combined weight is 22,000 but sometimes over 25,000. It does great. I did upgrade mine to a dually for more rear axle capacity (because my load in and on the van can top 4,000 pounds + tongue weight) but even stick it could handle that trailer as long as weight distribution is used.
