Doesn't sound like what you've got, but I had terrible issues with mine until I set a delay in the driver. The motor was super-slow and even geared at 27:1, not showing good torque. Set the delay, boom, happiness.
And you're probably even less likely to need advice along the lines of "toss what you've got", but man, if you want focus working toute de darn suite on your Pi, order yourself a
Waveshare Motor HAT
. For nineteen bucks you get a board that stacks right on your Pi and can control two steppers (two different styles of pin headers and a screw-terminal right there on the board, take your pick). It takes a standard 12V barrel connector and will run your Pi too (no need for a 5V supply for it anymore!). Kevin Ross's driver works out of the box