replaced speedometer driven gear with recommended 40 tooth and still not accurate...

What is the speed that the speedometer is reading and what is your actual speed???

Of go on the highway and do a steady 60 MPH then pass a mile marker, start timing when you pass the mile marker and see how many seconds it takes to pass the next mile marker while maintaining a steady 60 MPH...

Then post it up and I can do the math to tell you what direction to go...
Thank You!