[hemi43]

I worked in automotive manufacturing for 30 years, and what Keith said is correct. Those numbers represent the "options" on that given frame. Those numbers may specify if it's a 2WD vs 4WD, or if it's got certain holes or brackets for other things. Unlike the early 70's where there might have been a handful of frame variants, today there could be 50 different things that make the frames unique even though they look identical. On the newer truck frames they use a decal with both an internal numbering system and bar code that the line worker can see to determine which component goes to that particular frame. It still amazes me how such a complex assembly plant can spit out a vehicle every 50-60 seconds.