2004.5 Dodge 3500 towing capacity questions?

Grit dog wrote:
Well that’s quite the combo! You use 1st gear taking off empty I presume with those 40” semi truck tires?
Obviously 15k is a bit over the OE rating, but you’re nowhere close to OE.
15k behind a very similar truck (our 07 with a canned tune and clutch) pulls just fine. I’ve towed that much or more a few times when my company half ton just wouldn’t cut it, lol.
That truck with a tuner and a stout clutch (or even an OE clutch) will pull 15k with relative ease on normal size tires.
The brodozer tires combined with the tall gears (for that tire size) will hurt that ability considerably.
With that clutch and rappin it out in each gear, I surmise it’s doable. But it will be much easier on you and the truck with some normal 32-34” tall tires.
It is short trips, but if you have to start out on or pull any significant grades, I’d 100% ditch the semi wheels for a cheap set of 8 lug OE type wheels and tires. (If you haven’t done a permanent 10 lug conversion). If relatively flat terrain, I’d try it but be ready to use 4 lo for maneuvering the trailer to stay off the clutch.

The “rest” of the truck will be fine if your brakes and driveshaft are in good shape and the trailer has good brakes.

Yes, they are semi tires and if I have considered switching out gears for 4.33 gears. The most annoying thing with that tire/gear combo comes when backing trailers.

The project involves a water tank trailer (gooseneck) 15 miles emptying then 15 miles bach full. On the loaded leg I have modest grade. Nothing severe.

Thank you everyone for all of the replies. I appreciate your time and knowledge.