DPC3008 can't reach 50Mbps with Xfinity Blast! service

I just subscribed the Blast service in CO. And my modem is Cisco DPC3008. The speed test shows that it can only reach 27Mbps. I check the 192.168.100.1 page and see there are only 5 download channels available. Here is the information:
 
Model: Cisco DPC3008
Vendor: Cisco
Hardware Revision: 1.0
Bootloader Revision: 2.3.1_R3
Current Software Revision: d3000-v302r125532-121212a-L2VPN-CMCST
Firmware Name: d3000-v302r125532-121212a-L2VPN-CMCST.bin
Firmware Build Time: Dec 12 19:27:51 2012
Cable Modem Status: Operational
Wireless Network:


Cable Modem State
DOCSIS Downstream Scanning: Completed
DOCSIS Ranging: Completed
DOCSIS DHCP: Completed
DOCSIS TFTP: Completed
DOCSIS Data Reg Complete: Completed
DOCSIS Privacy: Enabled

Downstream Channels
Power Level: Signal to Noise Ratio:
Channel 1: 3.5 dBmV 39.1 dB
Channel 2: 3.7 dBmV 39.0 dB
Channel 3: 4.2 dBmV 39.1 dB
Channel 4: 4.3 dBmV 39.2 dB
Channel 5: 4.7 dBmV 39.1 dB
Channel 6: 0.0 dBmV 0.0 dB
Channel 7: 0.0 dBmV 0.0 dB
Channel 8: 0.0 dBmV 0.0 dB

Upstream Channels
Power Level:
Channel 1: 43.8 dBmV
Channel 2: 42.8 dBmV
Channel 3: 42.0 dBmV
Channel 4: 0.0 dBmV
 
Is that some problems with my modem?