Doesn't do it all the time and still goes perfectly straight with hands off of the wheel. Once it starts doing it it usually doesn't stop until you slow way down or make a hard turn.

Doesn't seem to happen at lower speeds.

When I had the car aligned after coilovers/new wheels/tires the tech said he couldn't get it perfect because the bushings spun.

Are control arm bushings and/or ball joints the issue?

99 sc400 138k miles

 

If it began soon after work performed, check that work and related parts for clues. Check tightness of bolts in strut tower, lug nuts etc.

check your brake pads and
check for sticking calipers too. There are degrees of sticking so it may not create a ton of drag and still be happening. Clean and Relube the caliper pins as needed. This aint a comprehensive list just a few ideas. Good luck and let us know what you end up finding out