AFE should be issuing a cold air intake for the 6.4L trucks.
Programming is expensive for 2015 - 2017 trucks as you need a programmer, a blank PCM and I'd highly suggest a custom tune. You can get that package now from Matt at Moe's Performance, one of our Preferred Vendors here at RamForum. I was very pleased with the results of the programmer and custom tune I got.
The gearset swap isn't a bad idea if you plan on towing a lot, especially if it's a heavy TT or 5'vr.
A freer flowing exhaust will always help. You can go as simply as swapping out the stock muffler for an aftermarket unit, which is what I did with a resonator delete as well, or go full catback single in/dual out muffler with new tailpipes. This will work only if you don't have the rear self leveling air system. If you do have that on your truck, you can't get a pipe over the rear axle on the driver's side as the distribution block, plumbing and such are located there. No room for a pipe.
That should get ya started...