I've read on here numerous times that if you are in the market for a new TV, buy one that can handle your next TT. OP stated they may consider going bigger on page 4. Not sure why you would look for something just a little bit better for your current TT if that's your thought pattern. Most 1500's are not going to have much more payload capacity especially if looking at the top of the line models. Maybe the OP should look at used 2500 gassers and be done with it. Otherwise, look for something used with a V8 sans options like 4X4, power seats and mega cabs.
As people have stated there are HD payload packages on certain Ford models, but you usually have to order it. If you are lucky enough to find a used one, you better be ready to jump on it. CarMax.com is a great place to look at used TV's - you can look at the features tab for a selected vehicle and from there see a link to expanded specifications where the weights, tow capacity and payload is listed.
I'm taking my own advice and will soon start looking for a used 2014 2500 Ram with the 6.4 Hemi as they are starting to become available off leases. I'm wary of the Ecoboost as I've had nightmares with a Turbo in the past - maybe they are better now, but I'm not drinking the koolaid on them - no bashing intended here Blue Oval fans!
OP should also be reading in the Tow Vehicle section - lots of great discussions in there on this subject. Good luck with your search