We just got this truck, 1987 K5 and it does not have tags on it yet, so we have only drove it off the trailer and into the drive way. (4 wheeled through the ditch). We live in Iowa where it is flat but there is rolling hills. This truck was bought with the Idea of taking it back to Colorado moutains. New K5 has 3.08 gears and 700R4 at 55 miles an hour that is 1300 Rpms and at 65 that is 1500 Rpms. Using the calculator. The tires on the truck now are 31" and they measure 1" taller than the original spare in the back that measures 30" It seems to me that the Rpm may be to low for highway driving, but then I am used to the old K10 with 3.73 gears. Any info on how well the new 87 with 3.08s and overdrive works. Our 96 Suburban has 3.73 and 4L60E (I like that set up with vortex) This seems to work good for us.