Out of the blue after changing tires, my 03 Burb QS started swaying while towing. When a semi goes by it yanks the truck & trailer all other. Never had this problem before. Had the original tires put back on and it re-aligned. Shop told me the idler & pitman arms had only minimal wear. Is minimal wear enough to cause this? Steering has a little "play" in it, could it also be a steering issue. Funny that I never had it until tire change, but now it's still here after returning to original tires(although new ones) Help!!! Shop told me to sell it, because Chevy won't even deal with it. Great truck otherwise and QS has always seemed to work great!

Avoid selling the suburban. There are alot of variables here depending on what your concerns are.

If it's truck swaying when a vehicle passes it could be the other vehicles speed/weight, wind direction/speed,..etc.
Tires are the same as the originals? Air pressure the same all around? Again more factors.
Depending on miles and condition all the chassis and suspension parts are in these could play factors too. (Rubber mounts are good and shocks are all in working order)
This probablly isn't real helpful but could be a few things to start looking at and narrowing it down if you choose to look more into this problem.