Sounds like a road crown pull. Your mechanic should be able to compensate for that, but you don't want to go too far, as it will cause a pull to the left on roads that aren't crowned as much or crowned the other direction (fast lane on the highway for example).
As far as alignments go, the basic suspension layout is the same all the way up to '87 on light trucks, '91 on Suburban and 1 ton chassis cab 2wds, and '95 on the G series vans.
