I'm going to jump in here as I have some experience on this as well.
2020 Ram 2500 Cummins 4x4 - CCSB
1" Thuren front coils / stock rear coils
Thuren Sway bar
Fox 2.0 shocks
LT285/65R20 Falken Wildpeak AT3Ws
No rear assist
Trailer;
2020 Nash 23D 28' OA 7,500 GVWR / weighed @ 6,820
Equalizer e4 WD hitch @ 100%
12% tongue weight @ 825 (up to 14% at one time)
This setup has porpoised from day one regardless of WD setup, weight on the tongue or weight in the bed. I've come to the conclusion that it's a coil spring thing. Trailer never sways, sits perfectly level and rides like glass since upgrading trailer suspension and tires. I left the truck factory rear springs because I tow, tow a lot in fact. Of the now 15K on the truck, almost 11K is towing and regardless of the tongue weight it has always done it. I've moved the batteries off the tongue (not due to this) and it didn't change it one bit. I've towed it with an empty bed and with 400lbs in the bed, doesn't change it. I added a 100lb generator on the rear bumper, nothing, nada.
I actually towed this trailer initially with a 2017 1500 CCSB Hemi w/ 3.92s and factory four corner air suspension. It never porpoised because the four-corner air suspension did an amazing job of controlling it. But the truck just wasn't enough for this trailer, had virtually no payload.
I've talked with Air-lift & SuperSprings and they both said the same thing, it's common on RAMs and must be the coil springs. SuperSprings recommended their
two-part Sumo spring setup as a solution, very similar to bags and cradles. I might go that way as I don't want to hassle bags, airing, compressors and such. Been there and it's a pain, I want set it and forget it.
UglyViking hope this helps some, you're not alone!