WTF

First, make sure there are no "goose eggs" on the steer tires. (broken steel belts) If you can, it's easier to see a bulging belt with the tire deflated. Just jack it up, let out the air, and spin it.
If the tires aren't out of round, I would suggest adding a bag of balancing beads http://www.tirebalancingbeads.com/ or 5 golf balls to each front tire.

 

Could you borrow a pair of (known to be good) steers and run them a little? I'd hope that would at least determine wheels/tires v/s suspension. Shaking makes me think it's in your wheel/tire. Keep TTR informed when you get it fixed, I'm curious.

 

I had a problem like this a few years back on a KW T800 I was driving. After replacing all the same stuff as you it turned out to be a cracked front rim.

 

did u ck king pins and king pin bushings. rebalance tires check brake drums and shoes use centering pins when mounting wheels and apply brakes when tighting lugs. it will help aline brakes and drums.

 

Did you check front brakes ?Might be out of round brake drums or brake hardware/shoe problems.

 

I work on a fleet of these trucks you need to add tru balance centering pins to center the drums and wheels,run kiaser no ream king pins aftermarket shocks and run a full either two axle or three axle alignment and some bead bags in the steers.also check the font u bolts and make sure theres no movement as i worked on one that had a 3/8 shim and the center pin wasent long enough to catch the lower block then check your rear suspension bushings center pins and u bolts

 

I use centrimatics. Don't know if it would help your problem. But I have gotten 221000 miles out of a set of steer tires .
They've been on my truck 1, 000, 000 miles.

 

Oh. I bought the truck new and I've never aligned it.. ever.