I finally got off my backside and fixed my speedometer reading error which for years read about 20% slow.
I found this site that sells a speedometer gear ratio adapter. Scroll down to item #54RA2. I talked to the tech who told me by using a GPS unit, make note of what the speedometer was reading at speeds of 30, 40 & 50mph. After a few jaunts down the country road we figured it was reading about 21% slow. So I needed a speed up adapter which they provide a 20% speedup.
Got it and it was installed in 15 minutes and now it reads very dead on. Yes, I could have gone through the exercise of changing out the speedo gear in the gear box but for a whopping $62+postage, I was up and running in no time.
Incredible how long I've been driving my truck with a wacky reading speedo.
Speedometer Gear Ratio Adapter