I'm definitly not the most knowledgable person to answer this question but i'll try to help in any way I can;
The early years (i believe 1970 to 72) first style are cool IMHO, they are getting to be hard to find around here, and they have really nice styling.
The first generation k-5's and the second generation ones up to 75 (someone correct me if I'm wrong) have a fully removable roof, and that is really cool too. K-5s after this only had the rear removable roof.
I think it was 81 that the newly styled fenders and hood came out for the K-5, and around this time they also got a new grill and headlight layout of 2 stacked on top of each other with turn signals hidden beneath the grill.
In 1987 K-5 came with throttle body fuel injection. This is better for gas milage, power, etc. This is the year that I have, and the only problems I ever had were mainly jsut not knowing what to do when it started acting up. If you are fairly knowledgable of TBI and sensors and all that stuff, thats good. If not, then you may need to get a code scanner if things go wrong.
Again, not 100% sure on actual year but I think it was 89 that the K-5 got the new style grill and headlights. Its the black grill with the side by side headlights above the turn signals.
As for knowing which year to buy, for me that would depend mainly on cost and what my uses would be. If you want better fuel economy, go for the 87+ years. If you are anything like I used to be and scared to death of fuel injection, go for the early years.
A nice feature of the 73-91 K-5s to me is the interchangability of parts. There are a lot of them out there so it isnt too hard to find most parts. At the same time, this is what makes the pre 73 K-5s kinda special in their own way, they are rare were I live, and I would consider them to be valuable.
Well, thats all that I can think of, and its very likely that I may have some bad information, if so let me know. I dont have much experience with these trucks, and there are many members on here who really know their stuff.
Sorry for such a long message, and good luck picking one out /forums/images/graemlins/thumb.gif
-pete /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif