I just read your other post about a clunk in the rear end. I spent the better part of a year searching for the source of my intermittent wander, and rebuilt the entire front end in the process (08 Yukon). Didn't cure it.
In the end, I decided to pause, and focus on my rear end clunk. I was coming up blank on that front, too. Had pry bars on every part of the rear suspension, loaded and unloaded. Nothing. U-joints tight as a drum. Spare tire tight. Just nothing. Rockauto had a sale on suspension components, and out of desperation, I ordered lower trailing arms and panhard bushings. Guess what? Clunk was almost hugely improved, and the steering wander was alot better. I then did the upper trailing arms, and the clunk was gone.
I can't remember who posted it, but there's a post on here somewhere about making a bracket that bolts to the crossmember, and u-bolting your steering rack to it. Eliminates any play in the steering rack bushhings. That completely eliminated my wander. I think each bushing had just a bit of play, and add them all up, and the front and rear just pointed a couple of degrees in whatever direction was easy. Add it all up, and it was a nuisance to drive.
Hope it helps