Thought I'd report on our first longish trip (1300 miles) with the SRT and compare to our '14 RT that we traded in, both towing the same 28' Airstream.
Weighed in at start of trip - with trailer loaded and hooked up with the Blue Ox weight distribution hitch (same one we used with the RT):
Front Durango: 3000 lbs
Rear Durango: 3700 lbs
So total on Durango SRT: 6700 lbs
Loaded weight of trailer: 6100 lbs (again, this was while hooked up to the Durango, so some of the trailer weight was on the Durango itself) I did not unhook and weigh the trailer by itself. This model empty is 5900 lbs, with no water. I had full fresh water 39 gals, so +300 lbs right there, plus all our "stuff".
Even with the occasionally wandering tires on the Durango (felt this only on the most rutted roads) the SRT was noticeably more sure footed and better at towing our Airstream, particularly at higher speeds. Note that I was totally comfortable towing it with the RT too. (I double checked and we had put 8K miles on the RT+Airstream combo, not 6K as I previously reported.)
With the RT, we would set our cruise at 63 mph - we would occasionally go higher to pass, but that was our max comfortable cruising speed.
With the SRT, on this trip, we set cruise at 68 mph, and it felt even more sure than the RT at 63. The fastest I went was about 73-74 passing someone and it felt totally stable. Going over 70 with the RT was much more of a white knuckle experience. On the SRT, no anxiety at all going that fast.
The RT did get a little over 11 mpg @ 63 mph.
The SRT got about 10 mpg @ 68 mph (so 8% faster for about +10% fuel consumed). I didn't have the patience to see the mileage on the SRT @ 63 mph.
I tried different steering modes on the SRT, when we got into rutty roads - didn't notice any difference. I did find by the end of the trip the wandering on the rutty roads didn't even bother me any more. Decided I will wear these tires out, and then replace with 4 season versions that aren't so soft and grabby.
I liked on the SRT that adaptive cruise control doesn't get too aggressive if you hit a hill and slow down 2-4 mph, it doesn't immediately downshift and burn fuel to maintain speed. There's a delay on that which seems to be more fuel efficient. When on single lane highways, due to construction, I would manual shift into 7th gear and it would maintain speed better, so cars behind me wouldn't curse me due to unsteady speed.
We usually took the steep hills in 6th gear, at near full speed, with occasion use of 5th gear on the very steepest hills. i would slow on these to about 63 mph, if it went into 5th gear. The big motor pulled very well - noticeably more torquey than the RT (which had the v8 hemi). With the RT, we usually ended up in 4th gear on the biggest hills, and had to reduce speed more.
The SRT is louder, but it didn't bother us. We didn't notice a bit of difference in sound when in Tow mode with noise cancelling on, versus in Auto mode with it off (supposedly).
I like the seats on the SRT better - they are a bit softer on my butt for the long hauls, maybe due to micro-fiber, although we really didn't complain about RT seats even though the leather is a little firmer.
We like the more "stick-like" gear shifter on the SRT, versus the rotating knob on the RT (which was never intuitive for me, even after 4 years with it).
We do have to put "92" in the SRT where we could get by with mid-grade in the RT, so this is more expensive to drive.
Overall - we are happy with the additional "margin" (on weights) we have with the SRT towing our Airstream. Really a nice combination and it gives us a more car-like vehicle when we arrive at destinations, and my wife a better daily driver, versus if we had a monster truck. If money were more of a factor, we could have lived with the RT (it worked fine for 8k miles with this trailer and we didn't know the difference), but we were blessed to be able to do this upgrade and we think for us it was a good call.
