I have a Ford 6.2 gas, that tows my FW very well. Forum member Dave HM went from a trusty older Ford 7.3 diesel, to a gas 6.2, and is very happy with it. For the size trailer and weight you are talking about, any of the big 3 gassers would serve you well. While they are more powerful than years past, the 6-speed transmission has made a big difference in gas truck towing. Of the 3, the only complaint I read about, is the transmission spacing in the Ram, especially with the 3.73 gearing. If wanting the Ram, get the 4.10.
Take them all for a test ride, buy the one YOU like, or just buy the new Ford with 6.2.:)
Jerry