Your steering problem is most likely the Ball joints.
The factory ford balljoints were supposed to be greaseless "lifetime". What they actually are is junk. If you get 10k miles out of them, your doing better than most!
Yard the ball joints out, and replace them with something with a grease zirk. I think I have Moogs in mine.
You might also need to take your steering box and either try to tighten it yourself, or take it to Red Head steering in seattle and let them go thru it. You can do it yourself by releasing the locknut and turning the adjuster like 1/16th at a time then take it for a drive. Too tight and you'll destroy the gears tho.
Red Head can also make it so your brake hydroboost doesnt steal all your power steering when trying to turn the wheel with your foot on the brake, such as when backing up a trailer.
You may also need to find a shop that really knows how to align these trucks. Just because its "in spec" does not equal a good steering truck. These trucks need a little more love in the alignment dept than your average econobox. You may even need a little caster shim between the springs and axle.
As for the ride, tires really make a difference on these trucks. Also dont run FULL air pressure unless your loaded. Knock 5 or 10 lbs out of them to soften the tire a little bit, without eating into your MPG too badly. More out in the rear than the front, as these powerstrokes are way nose heavy.
Your link to the 4-link setup is pretty cool. 1500 bucks is not a bad price. I paid 1700 just to convert my unit bearing hubs to standard fixed spindle. These trucks eat up the unit bearing on 35" tires if your wheel offset is too far out. Mine is pushed way out so I dont run the springs with my 35s. I hit the fenders instead... uhg.
