Nothing to do with the 1-2 shift, but as a FYI, there is a bulletin on the 2-3/3-2 shift...AKA: Tranny clunk
Information on 2-3 Upshift or 3-2 Downshift Clunk Noise #01-07-30-042B - (Jan 16, 2004)
Information on 2-3 Upshift or 3-2 Downshift Clunk Noise
2004 and Prior Light Duty Trucks...