Every blacktop road gets tire ruts, grooves, depressions where the left and right side wheels of heavy trucks and cars make contact over time. The road sinks under that repeated pounding weight. When it rains you can see water in the "two tracks" of the lane cause by traffic use. When you drive a vehicle with worn front suspension, out of spec alignment, poor shocks and tires, the vehicle will follow those travel ruts often fighting back to left or right when you stray out of the center of the lane, hit a bump etc.... Sounds to me like what you describe. Ball joints will often squeak, hubs will growl, tires will vibrate unusually, or maybe so subtle some never notice, until the vehicle is tracking all over the road surface.

Do a ball joint and bushing check for slop.

 

aren’t they governed? I don’t push my T because I bought it used but my 3 I would open up. It would engine brake a little over 90 the few times I’ve toyed with it in my youth. Been over 10 years. Recall it wouldn’t power back until dropped to about 70

 

You say you have more play in your steering wheel when you go up in MPH? None at lower speeds?

 

I have never seen these grooves / depressions you speak of, especially in the rain. honestly after some more driving I don't think its play at all, I think its just because theres so little play in the system and at high speeds the slightest movement and my brain auto-correcting perhaps causes it to feel like its loose?

 

Absolutely 0 play at low speeds, I think theres no play at high speeds and when I'm doing 75 or so the slightest movement causes it to move more and my brain over auto corrects, The colorados and H3s have some of the best steering in a vehicle I've ever driven, I had a 2005 220k mile colorado and the steering on that thing was super light and had 0 play

 

Did you check the steering shafts?