Searching forums, I found this thread which describes a problem similar to mine, but nothing was solved, or at least the thread didn't seem to have any resolution.

The current particulars:
2008 GSR
23,XXX miles
stock suspension*
18 x 9.5 Enkei NT03+N with some ****ty all season tires for highway purposes
custom exhaust
Cobb intake
COBB AP

*recently removed my AST 5100s to have them rebuilt

1.5 years ago, I put on my AST suspension, & after alignment, noticed the car would pull slightly to the right under acceleration (seems to happen above like 2500, or thereabouts). I cannot remember whether the car pulled a bit before installing the suspension. The pull wasn't terrible, so I didn't really think much of it, beyond being annoyed. I recently removed the suspension & switched back to stock so I could have the coilovers rebuilt. I had the car aligned, & then soon thereafter (few weeks, & maybe 100 miles?) switched tires.

Fast forward to the past week-- I've noticed the pulling is even worse. It happens when driving at normal speeds. Frankly, it's scaring the crap out of me.

Basically, when I'm driving, when accelerating, I notice the wheel turns to the right about five degrees, but the car basically stays straight. If I pull the wheel back to center, it veers sharply left. The issue also happens when cruising-- I'll be at whatever the highway speed is, & then I touch the throttle to go around a car & the wheel turns. When I push in the clutch or let off throttle, the wheel returns to 12 o'clock. The wheel seems to turn even when I'm using cruise control & the car accelerates to maintain speed.

Today, when exiting a freeway, the road turns to the left & merges onto another highway. While going around this bend, the car was fighting me violently trying to pull right & the center cluster gave me a slip/ traction warning. I tried another curve with the AST disabled (having held to as-fully-as-possible disable) & the car still fought me, but I didn't get the slip/ traction warning.

I cannot remember hitting anything that would have exacerbated my problem. The issues seem to happen everywhere, independent of speed or road condition (ie just under acceleration-- when I let off, the wheel goes back to normal).

Any ideas what this could be? I don't want my car to feel scary!

PS: Apologies for the long post-- I'm trying to be as concise as possible when describing the problem.