My e150 front end shakes at cruising speeds. Has brand new tires and the best balance wheels are up front. I got the van on jack stands check for play on the tie rods and ball joints it all seem to be good and tight.
The only I did notice was that the both wheels move quite a bit from side to side and the culprit is the gear box. I removed the drag link from the Pittman arm at gear box and then i was able to move the Pittman arm at the back and fourth about 1/8 to 1/4 of an inch its not a bad Pittman arm cause the movements comes from the gear box itself.

Can that back and fourth movement be adjust by simply adjusting the Allen bolt and nut on the top side of the gear box?

 

Nope. You need a new steering gear.

 

No, really thank you for response. Started pricing them so far Advance Auto has the best price on a manufacturer one at $174.00