I would start by follwoing the steps here to determine how the signal input to your router is:
http://www.dslreports.com/faq/16569
If your results are less than 200 Mb/s, you may have a problem in the coax feed from your ONT to your router.
In any case, I would call tech support and see if they offer any help. You might urge them to send you a replacement router if they don't see anything else wrong with your system.