I have ran rancho 9000s on the 2500 since 280,000 miles. now to 852,000 miles. This is on a heavy diesel with a 90 gallon fuel tank in the bed, used to pull campers all over North America. The front shocks i set at 6, been on the truck almost 600k miles now. And the rear, which have been replaced a few times do to leaking, I leave at 7. Also have air bags on the rear. The rear ride is bouncy without a trailer, but I am very satisfied with trailering ride.
If i wasnt hauling I would perfer the rear to be at 4 or 5 setting. And do to the amount of time i have had the shocks on the truck the plastic dials have siezed. Im afraid to try to turn them.