Help! Trying to calibrate my speedometer.

[Botietruck]

I need some input here. In an earlier thread I made mention that my speedometer was off about 10 mph. The cruise on my wife's van was set at 60 mph and my truck was running 50-52 mph. I pulled the speedo gear out of the trans. tonight and it is a 24 tooth gear. I'm thinking I should get a gear with more teeth. The parts book lists the next higher number as a 25 tooth gear, and the next one above that gear has 34 teeth. Am I thinking correctly in that I will need a gear with more than 24 teeth? I believe the 34 tooth gear would be too much. Any thoughts??