that is correct. with adjustable resi you can tune your ride for firmness. However, there's only so much you can do with adjustable resi.
that's why for best performance, shock tuning is preferred. Shock tuning is done through adjusting the shims inside the shock piston to get the off-the-shelf shocks to better match your truck's weight, your driving style, and the road/ trail surface you are constantly on in terms of compression and rebound, while adjustable resi fine tunes the compression and rebound based on your need.
Visit here for more information regarding shock tuning and adjustable resi
Regarding your choice:
I am assuming you'll be using it for offroad use and probably will want to go fast off pavement. For that purpose, either King of Fox will be great choices. However, King only offers mid-speed compression adjustment and currently has a long lead time. On the other hand, Fox 2.5 Elite Series offers both high and low speed compression adjustment (means more fine tuning ability) and does not have that long of a lead time as King.
Now, BDS 3" utilizes Fox 2.5 series (with DSC) for front, and although Fox advertises it as 2-3" lift, I personally don't recommend running full 3". This is because you are actually giving the shock less "reserve" to travel when you go through stuff by increasing preload to create that 3" lift, which means less bump absorbing capability. Ideally, you will want to do about 2.5" for the front and 1" for the rear for maximum performance and on/ off pavement comfort. How do I know? I had a 3" lift as the set was advertised for 2-3", and it was very harsh both on and offroad. I then cranked it down to 2.5" and it improved the shock performance a lot. This was with Kings on my 4Runner. I know it's different platform different brand, but same idea.
Alternatively, if you absolutely have to get 3", get it touch with Thuren Fab and get
this set from them. These are custom tuned to your spec and will perform a lot better than any off-the-shelf shocks, including Fox and Kings. They are also more knowledgeable with shock performance and tuning, as the owner Mr. Don Thuren is very experienced in high speed desert runs using Ram trucks and can give you his honest opinion.