G3 rpm/gear ratio

at 65mph I am about at 1,900rpm, 2,300rpm at 80...

If you had 3.55s, 0.69 OD and turned 1,800rpm at 80mph, you would have to have a 36" tall tire...the correct calculation is 2,368rpm using the 27" tall tire you reference earlier.

Ran the numbers again. You are correct.