Neophyte here! Just took my 1999 in for an alignment, I asked for a 4 wheel alignment but he told me I only need a thrust angle alignment. I must admit that I am on a steep learning curve here, I love these trucks but don't know a lot about them. I do all the minor stuff myself (oil changes, rotations etc.) and would do more if I knew how. So, why only thrust angle and not 4 wheel?