crispy:
I agree that the official motor driver is not the most ideal for my application. I already have one on-hand though, so I have an incentive to try to get it to work before buying additional components. The motors I'm using are low-current low voltage motors that come with the Tamiya double gearbox so the current limit should not be an issue.I like the look of the pololu driver you linked, I will keep it in mind if the shield does not work out.
Thanks again for your help.
Actually, those low voltage motors are typically worse. Higher quality, higher voltage motors will typically be easier on an H-bridge and keep things cooler. Just keep your fingers and flammable material away from the L298N 
And if you do decide to get another motor controller, consider the serial interface version. It's far easier to connect and use, control using just two wires no matter how many motors you have, and simple library commands. I have a half-written updated library for it that simplifies things even more.
Tim