download speed very slow, upload speed surprisingly high

Lately my internet speeds has been seriously acting up. Here's a snapshot from Cox's speed test.

My download speed is much slower than usual (I usually get around 40-50mbps) and my upload speed is surprisingly fast (I usually get around 20mbps).

I tried removing my cable splitter and for a bit I thought that fixed it (I shot back up to 40mbps download) but within an hour or so it was back to less than 10mbps. Frequently it was as low as 3-4mbps.

Here's my modem stats:

Model:                      Cisco DPC3010
Vendor:                     Cisco
Hardware Revision:          1.0
Bootloader Revision:        2.3.0_R1
Current Software Revision:  d3000-v302r125533-120716a-COX
Firmware Name:              d3000-v302r125533-120716a-COX.bin
Firmware Build Time:        Jul 16 17:16:46 2012
Cable Modem Status:         Operational

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:    5.6 dBmV        38.0 dB
Channel 2:    4.8 dBmV        37.5 dB
Channel 3:    4.8 dBmV        36.5 dB
Channel 4:    4.6 dBmV        36.2 dB
Channel 5:    3.7 dBmV        37.1 dB
Channel 6:    3.2 dBmV        36.2 dB
Channel 7:    2.7 dBmV        32.2 dB
Channel 8:    2.0 dBmV        31.4 dB

Upstream Channels
              Power Level:
Channel 1:    40.7 dBmV
Channel 2:    41.4 dBmV
Channel 3:    39.2 dBmV
Channel 4:    39.4 dBmV