Most steppers use 1.8 degree steps, not .9, so there are 200 steps per revolution. Are you using a halfstepping drive? Microstepping smooths out the motion, but it doesn't make the router more accurate.

80 oz-in is not a lot of torque, and stepper motor torque falls off rapidly with increasing speed. So even if your motor is rated at 80 oz-in holding torque, that doesn't mean it will be able to reliably lift that load at the speed you want.

NEMA 17 motors are too weak for anything but the smallest and slowest cutting machines, although they can be used for light machines which don't have to deal with cutting forces, like 3D printers. If you want something suitable for a reasonable-sized router that's useful for cutting wood, I'd say go with NEMA 23 or bigger.

Andrew Werby
www.computersculpture.com