When they went to the 6 speed transmission they no longer offer the 3.73 rear end. I think it may come with a 3.55 but not certain. I would prefer something higher than a 3.31 as I think it is easier on the tranny to have a higher rear end but they all seem to be that way in the people movers these days.
I would guess that a trailer that grosses 7500 pounds is going to be all you will want to tow. My Expy has the same rating and anything over 7000 is pushing it, even when the Expy is empty other than the two of us.
Even in a pick-up the max tow weights are not really applicable in a travel trailer. You might get there towing a flat bed trailer but not a big box.