I have the 3.73 and do a fair amount of towing. The 19 ft bay boat will be no problem at all.
I tow 6000-7000 lbs regularly, and I just lock out 6th gear on the heavy loads. It's basically the final drive equivalent of a lower speed rear end. With 6th locked out it runs at about 2200 rpm at 75 (which is nothing for a gas engine). The tranny runs cooler because it isn't downshifting on hills and it actually gets better gas mileage since the engine isn't lugging.
If you towed heavier loads most of the time, I would say the lower speed rear. But you don't so get the 3.73 and just lock out 6th when you get your TT.