When I was looking at CST I talked to a rep there and he was telling me about the adjustable reservoir version that wasn't on their site, but it was a while ago so perhaps they're not double adjustable, I thought I remembered that though.
As a final update-
When I first put sulastic springs on the back I felt it made the rear a little bit softer than the front, so the front was the more harsh part of the truck. After the softer front springs and Koni front struts l, I determined it does ride nicer and again, I feel the rear is a bit harsher again. As a reminder, at this point I still have Bilsteins out back.
After a week or so of this, I decided to put the rear Koni shocks in. The truck rides even better yet. It finally rides like it should, how I remember previous Chevy trucks when they were new. Comfortable, good balance of soft and complacent. Firmer than something like a minivan or crossover for sure, but not harsh. I no longer notice even the tiniest of pavement marks, cracks are felt but not really noticeable or distracting.
Summary of modifications-
Front -
-4wd Tahoe front springs. Ended up lowering the front 5/8". My truck never say really really low up front like I see some trucks though (seems like more often double cabs)
-1" lower strut spacer, so the front sits about 3/8" higher than stock.
-Koni front struts.
Rear
-Sulastic shackles. - these essentially give the rear leafs a 3rd stage. They make the rear springs softer until they reach the limiter then they have no real effect on ride quality. I have firmer than normal ones but since they replace a solid shackle, they do make the rear springs softer and better isolated.
-Rear Koni shocks.
These mods may not be for everyone and It's about $875 (I spent a lot more doing my trial and error) but I paid too much for this truck to not like the ride. Since I live in the north we have a temp swing of over 150 degrees summer to winter and the roads get rough. If I lived in the south, where I noticed roads are usually smoother maybe I'd like the Bilsteins. I don't care for the 5100s myself, but if you like a firm ride they're probably a better way to go.