Towing my new 38RSSA

You should always be ready for the trailer being at GVWR - in your case 21,000. For a CC LB dually, either 3.73 or 4.10 is rated for over 21,000. Me, I'd go for the 4.10

If you're going to be putting that aux tank in your new truck, remember that's a lot of weight that comes out of your payload.

BTW, it's Cummins and Aisin.

I also have the 4.10 with Aisin. With the Aisin you also get the High Output engine, lower first gearing and a bigger differential with aluminum cover for heat dissipation. I did not order it with air suspension as I have never liked them on PU's. I put some summo springs on it and it stays perfectly level with my 3950# pin. Ride is fine. No air to leak.

I have a 2016 DRV RSSB3 , GCW of 19K, so you’re is heavier. I have truck in my dig and am full time. Towing now between WV and TX. Truck tows very well on steep mountainous curvy roads and on flat land, I have to admit, it’s like it’s not back there, ( NEVER thought I’d say that). I like the rear air assist and the medium duty Aisin transmission. I have the 4.10 gearing which gives you the highest GCWR. I’ve read on here at times a lot of people think the 3.73 is the best of both worlds, but am hearing now a lot are staying with the 3.42gearing. Guess it’s your choice. I’m in some steep secondary rads at times when in VA, TN, WV and NC. I’ve had 4.10 gearing in Ram trucks since 2010 and never an issue. It’s what I tow with and I wanted the 4.10. Just preference. Others have theirs. I would get the puck system where you can drop a hitch in.. just makes it nicer, as well as the cargo camera.. nice for hitching up the 5er. Hope this helped

Jim