Gigablast service providing 290 mbps...???

I live in Litchfield Park, AZ.  I bought Gigablast service a few months ago.  The service is pretty good and reliable.  However, I'm not getting the speed, or even close, that is advertised.  Is there something I can do with equipment or positioning in my home to improve my speed/service?  I have an ARRIS SURFboard SB8200.