Re: Black Diamond 4\"lift
4" is perfect, just about all you need for most trails.
A couple things to note though. How big of tires are you running? Less than 35 inch doesn't need dual stabilizers. Having them just makes the steering very stiff.
One other thing, not sure your year of truck, but if its '73-'87 style, I am guessing you picked up a raised steering arm as well to correct the geometry. Before installing it, remove the old one and place them side by side. Measure the relative postions of the ball joint hole. The new one should be 4" higher than the stock one. I had a BD one and it was 5" higher and caused brutal bumpsteer. I traded it for a Rancho arm, which measured correctly 4" and no bumpsteer.
Just thought you'd want to know.