How many of you calculate your fuel load in reducing payload? Anyone? Well, you do NOT have to if you do. The payload is figured "including all fluids." So, for some, particularly those with lower payloads, this is important. AND, don't forget a dry hitch weight does NOT include your propane tanks or batteries OR your weight distribution hitch.
These two "issues" are the ones I see as the most confusing for NEWER people to towing. So, pick up a couple hundred lbs by not worrying about your fuel load and lose it by accurately figuring your tongue weight... Two group 24 batteries and two full 30 lb propane tanks are right at 200 lbs (195 to be exact.) A gallon of gas is right at 8 lbs so do the math based upon gas tank size if you want to get specific. If you have the 23 gallon tank, AND TOW, you will be stopping about every hour just so you know. The 26 gallon isn't much better. A 33 gallon will get you around 30 to 45 minutes more between stops for fuel. Based upon my experience having had both, the difference between a 3.21 and 3.92 rear end on fuel WHILE TOWING is neglible. The 3.92 is "better" when towing, but the 3.21 is just fine as long as you are not maxing out your weight, but if you are doing that, then you are likely OVER payload. I had a 2013 Ram 1500 with the 3.92 and 5.7 hemi and the 3.55 rear end and personally think that is the best mix imho. I wish the 3.55 was an option for the 5.7. I shoot for about 80 to 85% of my total towing weight for a trailer and am fine towing at max payload. This is simply my opinion from 16 years towing with various size rigs behind me and three different trucks and an SUV.
This website (fixed quite awhile ago) will tell you your truck's payload by VIN number.
https://www.ramtrucks.com/towing/towing-guide.html Click on "Look up my vehicle" and there it is... If you want, you can double check by doing the math on your sticker on your truck. IGNORE the tables, charts and graphs.
AND remember, salesmen seldom know squat about towing and concentrate on what the literature says and it generally says you can tow the eiffel tower, no problem... NEVER believe a salesman. Get the VIN and look THE SPECIFIC truck up.
Edit: OH and read this thread all the way through.