Shakes or Wobbles problem
2006 Nissan Frontier 6 cyl Four Wheel Drive Automatic 44000 miles

I recently purchased a 2006 Nissan Frontier 4x4 and noticed that it rides with more vibration than other models i test drove. I thought it might have been the two different sets of tires that the dealership had on it so I didnt think too much of it. I just replaced all 4 tires and it still didnt seem to get rid of the problem. Once I hit about 40 MPH i noticed it. Also when I go to brake at a stop sign or stop light it shakes or vibrates more than other models I test drove. Could this be an alignment issue? Or do these trucks just ride different? Any information would be helpful.

thanks!