I never could understand why my '87 K5 was such a 'dog' until I was getting the rear end checked out and discovered it had 3.08 gears in it. The overdrive was always kicking in and out whenever I'd even drive over a bridge, I suspect because of the high gearing. I can't believe it actually came from the factory like this, but ......... Also, I had about a 9 mph slow speedo error at 50 mph so I knew something had to be wrong. Solution: I bit the bullet and just installed Auburn Pro-Series Posi units front and back with Yukon 4.11 gears. I sort of thought the gearing change might get me pretty close back to normal but now I find I have an error of about 12 mph fast at 60 mph. I'm running Pro-Comp 31 x 12.50's on Rock crawler 15x8" rims and strock supension. I'd like to go to 32's or 33's but don't want to lift it. Question is: what do I need to get my speedometer reading correctly again. This is my hunting vehicle so it's not a big deal except that I have a special insurance rate for it if I don't put on more than 7500 miles a year. Now I actually have a 21 mph delta from what I had before so I need to get it changed. Anyone out there running the same gears and tires that can give me a part number or ? ? ? for the speedo gear ?