The door tag says 4332# payload and 12,300# GVRW. I don't know how to determine the max camper weight. I looked at the camper guide a while back (have it printed) and the numbers were well below anything listed for payload typically. The guide I have says 2970# or 4339# for two that look identical on the chart.
If I look at the ram truck builder site:
https://www.ramtrucks.com/assets/towing_guide/pdf/2016_ram_3500_towing_charts.pdf
I see on page 5 for 4x4, SRW, diesel, 68RFE:
6.7L CUMMINS DIESEL A6 68RFE 3.42 12,300 4,480 7,825 4,854 2,970 6,000 7,000 25,300 17,010
That's essentially what the door tag shows (difference is options I have over standard).