I was wrong about everything! (Suspension problems, part 2)

Go to a truck spring business. The one in my area is awesome, they know their stuff. What you are trying to figure out, is what they do every day. And they do work on pickups and vans.

Really, I would head there asap, fully loaded. I know you like your mechanic friend, and his recommendation may work. But I'd go to the real pro. Your rig needs some serious work, not some band-aid that might work.