I agree with Robin2 that the L298 is a problem. Most people can't even get 1 ampere per channel before they start to overheat and shut down. You should try the Pololu chopper drivers but even they will have a hard time with your motors (which are rated at 1.7 amps/winding) without extra cooling. Be sure to set the current limit to 1.5, or even 1.2 amperes.
For tests showing the poor performance of the L298 drivers, see: The Motor Driver Myth — Rugged CircuitsRugged Industrial Arduino Microcontrollers