2012 Tacoma Sport Steering Wheel Shake

Hi Guys, I'm just signed up on this forum and I know this issue has be discussed here and I've read all the post. I have a 2012 Tacoma with stock 17'' wheels running Dun-lop AT20 tires,my steering vibrates or shakes at highway speeds.When I test drove it drove smooth as silk for about the first 200-300 miles.This issue comes and goes I can a couple of days with no issue and then it's back totally varies. My local dealership has rotated and balanced and torgue lug nuts to 90lbs. This lasted for about 2 weeks now my vibration / shaking is back. They are going to look at problem again on June 4th when the district service manager comes in. Any suggestions would be greatly appreciated, I'm now considering looking into dealer buy back or lemon law as a option.