Update: I installed the K&N FIPK kit on my 2015 3170DS about 1500 miles ago.
I regularly travel the same route with my RV, which is 230 miles each way. The last 1/3 of the trip involves quite a few hills requiring me to either let the RV downshift 2 gears (if I left the cruise control on) or turn off the cruise and slow to around 55 to avoid downshifts.
.75 MPG better (I pull a 4,000 lb. trailer all the time)
about 50% less shifting while using the cruise control
it will pull hills in 4th that used to require 3rd to maintain speed at 55mph
Considerably more intake noise when under a load. For example if you are climbing a long gradual hill (where the trans stays in 5th gear) with the cruise on at say 60-65 mph the intake noise can get pretty loud.
Overall my family continues to be very happy with our purchase of a 3170DS. I also added a small fan that plugs in the dash power port that helps keep the cab more comfortable on long drives with the just the rear AC going.
We are currently building a new home so we are not camping much this year.
This fall I will be building a pole barn (24x45x14) to store the RV so I am excited for that. And will likely be looking for advice from those who have built RV garages in the past.