I just put the BF Goodrich KO2 all terrains on my 2015 bighorn. I did so on many recommendations by folks here(Thunder horse) load range D with 58 psi cold when towing, and 45 when empty. I pulled my 7000# keystone Bullet across the country, and have been very satisfied with their performance. Both on and of road.
I also added 1000 series air bags inside the coils, and run them about 13-15 psi when towing. Any more pressure in the bags, and it starts to feel like you're in a small boat coming in with the waves.
2015 Bighorn hemi 8sp ,3.21 quad cab GCM.