Speedometer Gears for 3:08

I have a problem with my speedometer. I have a 350 turbo, 3.08 gears and 26.5" tall tires. When I am driving, my odometer reads 2 tenths faster than the mile markers read. So, if I go a mile, my speedometer says I am going 1.2 miles. I have the speedogear that is for 3.08 gears in my tailshaft. I bought it a few years back and am just now on the road with it. I am now seeing that there is another gear with 1 less tooth than what I am running. Would that fix it, or is there something else up?

 

find out what DRIVE gear is in your ****** , then go to this website and type in all this information...it will tell you what DRIVEN gear you need. it also gives you the GM part number. you can get it from any dealer.


http://www.tciauto.com/Products/TechInfo/speedo_gears.asp

 

All I can add to what 36-3window said is that if you have access to a gps you can get an exact speed and note the difference. One of the hand helds works great for that but the ones to navigate your car works too. That will be more accurate than going by mile markers.