[Grim Reaper]

Good stuff. Few things to add.
Like the poster above said the gas door was a mid year change at some of the plants. The K5's also got a floor change in 78 that gave rear seat passengers a foot well. This also alowed for the Fold and tumble seat for the rear to alow for a quck wat to get full cargo space.
78 was also a majore electrical change. Sometime Mid year they discontinued the glass fuse fuse block and went to the Spade style.

The 241 replaced the 208 in 90.

90 and 91 power mirriors was an option on the Blazer and Suburban.
91 the Suburban came with the 4l80 in the 3/4 ton

89 was a style redoo getting a new 4 spoke steering wheel over head consols in the Sub, new grill treatment to try and make the Subs, Crews and Blazers look a little more like the new body trucks.

The 4 year carry over had several reasons. Not the least of these was the military contract to provide trucks and truck parts for 10 years.

The 89-91 had a 30 spline front and rear axle. there were 27 or 28 previously.