Premier Internet Speeds

I was only receiving about 28mbs down. I was on the phone with a Representative and was so that I need to purchase a DOCSIS 3.0 Modem to get into the 50mbs range. I just bought the Motorola SB6141 but i haven't seen any change in my speed. Can someone help?

http://www.speedtest.net/my-result/3122893235