Just bought TRD springs, had them installed. Noticed that once I hit 60mph, or above, the steering wheel vibrates significantly. Not violently, but enough to annoy the hell outta me. Took it to Firestone (cuz' they're within walking distance from my house), they balanced the tires and gave me an alignment (which is what I figured was the problem). Anyway, after this service, the steering wheel still vibrates. Any theories as to what the prob might be?

hmm, vibration is a balance problem. If it tracks to left or right its alignment if it vibrates or shakes its balance maybe u should have them check it again.

mine did that at about 50 + i had my wheels re-balenced (for free from discount tire) and it never did it again. however it could be that you have blown shocks now due to the lowering, are they stock shocks. if so you'll probilby need higher end replacements, direct replacements will just blow agian.