You are correct about 2X shock from the factory. None found. When I was a hard core jeeper, i did a lot of work on leaf spring suspensions on a variety of machines, including about a dozen SOA’s (springs-over-axle) which adds another twist. You are good aiming for many and thinner leaves for your RAM. This was the SOP paradigm for WW II Jeeps and domestic 4WD’s up until the 1970’s and beyond.
My current Dodge Cummins has a unique rear suspension which was added onto, not started from scratch. It came originally as the camper package for the 2001- single rear wheel 2500 4WD. At the time, there was no 3500 SRW Dodge, so this was the defacto version with a thick upper overload (or secondary) spring, which got the payload range up to 2600 pounds. This set up carried my Lance Lite camper just fine but I wanted to experiment with more leaves in the upper pack. I bought a set of Stable Loads, essentially a rubber/composite block which allows the overloads to engage sooner. A friend asked me if i would like his upper overloads from his 2001 3500 Dodge, which were a pair of thinner leaves on top per side and had just a little more capacity than my thicker single spring. Now i have 3 upper overloads. When I lifted the front end 3 inches, the rear was now looking lower by comparison. I looked around and found a pair of 1800 pound, single leaf helper springs: rather thick but flexible enough and added them to the pack now at 8 leaves per side. This required longer U bolts. Along the way I rebuilt the factory anti sway bar with soft parts.
Now it gets weird. I found by trial and error that i now have a triple range suspension. The single leaf helper takes most of the small changes of the suspension, whereas the uppers only come into play when I have a full and heavy load. The stock leaves work in the middle. Remember the only difference between a 2500 and 3500 in this era Dodge was the rear axle is narrower for the duals and hub extensions in front to accept the 7.5″ back spacing the dualies use. Oh, and those upper overloads. I’ve carried 5K pounds of crushed rock in the bed (for 20 miles) and the truck suspension acted normal with all 3 subsystems operating and in control with minimal sagging. The only thing i noticed was the stopping power going downhill was diminished. After a trip to Anza a couple years ago I noticed in this video https://www.dropbox.com/s/bfj5y93wsd7vfkw/jefe%20does%20sand%20hill%20at%20dry%20wash%20of%20the%20devil%20Anza.m4v?dl=0
that i had too much up and down springing on the whoops. I’ve done dual shocks before with light and flexible springs and a lot of shocking basically to allow more range of motion when you get the axles twisted up.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.