GM started the 60 in 78, maybe 77, thru 91 in the crew cabs, but K30s and K35s only. Bout the only differnce in those years are the axles shafts, 80 and earlier had the tapered inners, whereas the newer ones had the same size diameter on the whole shaft, or close to it. The 14ff didn't have too many changes, but in 87 or so they went to the new design, don't remember what it was, but easy to tell by the ribs on top of the axle, sorta looks like coolng fins. As for the best years, anything newer as it might have less abuse, but can't always go by that. Probly the military trucks, 4.56s and sometimes a T/L, and 14ff with 4.56s and a Detroit.