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

Heres a gear chart from brewers performance In regards to tire diameter, and final drive ratio to determine speedometer gear. If you have a 225 60 R15 which is a 15" tall tire,

((( however i cannot decipher what you have tirewise in your post. Is it a 50, 60, 70 series?)))

and a 3.91 rear gear it says 41T

View attachment 1715600342
Thanks. That's what I was thinking (41T) before buying the the 40T but Mancini insisted it was a 40T