Yeah that's it / the one I was thinking about.
Theres another out in (I think) Pa. I've talked to.
I was on the fence about where to get the ones for my 01 Durango, both places listed "HD" option, with same capacity, but the place in Pa had the heavier capacity on 5 leaf (same number of leaves as original springs /and their std duty) general had as a 6 leaf assembly, I got the 6 leaf. I dunno if they used a thicker leaf as the 5th leaf?

I've added a leaf on many of my vehicles, and never had the "lumber wagon effect" on any of them the way I do on this Durango. I've since bought 5 leaf springs for my 78 fury from them to replace the original 4 leafers, and no lumber wagon on that, it actually much better than the originals ever were.
I took those originals off about 10-12 years ago and took them to a spring shop and had them "re arched" and that didn't last a year. I ended up having to buy some air shocks for it and putting them on in a parking lot while we were on power tour that year, with the 5 leaf units and regular shocks it rides so much better than the original 4 leaf + the air shocks.