Looks to me like your smoothing groups are messed up. Using Max or Maya? If you're using Max go into Edit Poly > Polygon Smoothing Groups > Click Auto Smooth The problem is that your smoothing groups are wrapping around to another section of the mesh. Auto smooth should get things pretty close. You can assign your own…
Spid, my guess is that your smoothing is trying to smooth from one side of the door, over the top, and into the cab side. If you put a hard edge along the outside top of the body, it should get rid of a lot of those lines.