I am considering buying an F150 Ecoboost crewcab 6 1/2' bed to tow my ski boat. I have looked at one with the 3.31 differential. The combined weight of the boat and trailer is 4500#. Will a 3.31 meet my needs or should I go with a 3.55 rear end?
I always recommend the 3.73s to everyone that will tow. The MPG loss seems to be nominal from real life examples on this forum. To answer your question the 3.31 will be fine, but my recommendation is the 3.73s because if and when you upgrade or need to tow something larger you will be good to go.
I have 3:31 and tow a 21' Rinker on a tandem trailer and it pulls it very well. I lock out 6th gear and it pulls it without shifting out of fifth up hills easily, running 2,000 rpm at 70 mph. I thought I was buying a truck with the 3:55 (that's what the online option list read) but it ended being 3:31, it seems to work just fine but I would probably go with 3:55.