Flummoxed

I'm having a slight issue with my 09 cobalt lt steering. While at highway speeds I'll notice my steering will shift slightly, not a serious amount but enough for me to notice. Going down a straightaway or going around a curve it feels as if a strong gust a wind hit my car and I have to correct the steering slightly.

Replaced both control arms about a years ago because of bad bushings.
Replaced both front wheel hub assy about 3 months ago because passenger side was starting to squeak.
Replace rear passenger wheel hub assy about 6 months ago because of rumbling sound from wheel.
New tires 2 weeks ago.

The steering problem has been going on for a while but I normally don't drive 75/80 mph on interstate like I did this past weekend, which made it more noticeable.
Any ideas what I should look for next time I lift the car up?