1996 Lumina LS with 3.1. Car slightly pulls to left even after new front tires & alignment. The real problem is you can be traveling down the road in a straight line & all of a sudden the wheel pulls one way or the other as if the car is in a groove & wants to go it's own way. It's almost like a midget is hiding out in my wheel well & without warning just decides to slightly turn a tire without me turning the steering wheel. Of course I just turn the steering wheel back & everything is fine again. This isn't a violent manover but can't seem to figure out what is causing it. Any suggestions?

As part of the alignment, was the steering rack checked for wear? Was it a four wheel alignment, complete with rear check/adjustment? Rear wheels can track oddly and impart steering forces (thrust) on the front end as well.

That kind of bump steer effect is often from worn/loose steering rack to body mounts, bad subframe to body mounts, seizing strut bearing plates, etc.

That kind of problem usually seems minor until the affected item breaks or seizes totally and you loose any control...don't take it too lightly...

And it could be the rack itself going bad, seals will leak internaly and push it side to side slightly without you turning steering wheel. Scary when it happens isnt it? had them do this before, expecially on older Omni/K cars.
And FYI, i bought a remanu. rack from Advance Auto for my 91 i had, it lasted less than a year before puking all the PS fluid out of it, total junk. So uless you do have something binding or loose, or whatever, me..... id rather take a chance on a original junk yard rack if i couldnt afford a new and not rebuilt one. Unless someone someplace remanufactures ones better than Advance, which wouldnt be hard to do.

A good alignment shop is your new best friend...

Even a worn tirod end could cause the prob. Had it happen on my '93 Euro.

Worn out tie rod in a lumina?!?! No way! If the shop from which you bought your tires and had the car aligned is competent, they would have checked the tie rods, ball joints, etc. before they corrected any angles. Like I said...if they are competent.