Very unstable connection

For the past week or so my connection has become extremely unstable. Running PingPlotter to various sites has the same result of wildly fluctuating ping, from 10ms up to 300+ms and this happens every few seconds in some cases.

Its an intermittent issue, there are stretches when its quite stable. Its been getting worse though and tonight it has been spiking for hours and the gaps of stability are few and far between. 

This data is with the modem (SB6180) directly connected to the PC and no applications running:

Target Name: www.google.com
IP: 2607:f8b0:4002:802::2004
Date/Time: 4/16/2016 10:18:51 PM to 4/16/2016 10:23:51 PM

Hop Sent Err PL% Min Max Avg Host Name /
1 301 0 0.0 6 751 56 [2600:8800:ff10:900::1]
2 300 77 25.7 6 702 83 [2001:578:809:107::24]
3 301 1 0.3 10 675 87 [2001:578:802:104::6]
4 301 0 0.0 22 637 102 [2001:578:1:0:172:17:249:33]
5 301 0 0.0 22 587 100 [2001:4860:1:1:0:58f5::]
6 301 0 0.0 22 536 98 [2001:4860::1:0:c432]
7 301 0 0.0 23 488 99 [2001:4860::8:0:7a1a]
8 301 0 0.0 46 614 118 [2001:4860::8:0:2c9d]
9 180 0 0.0 66 511 145 [2001:4860::8:0:52bb]
10 301 0 0.0 65 652 140 [2001:4860::1:0:c90f]
11 301 0 0.0 66 626 136 [2001:4860:0:1::164]
12 301 0 0.0 66 857 101 atl14s08-in-x04.1e100.net [2607:f8b0:4002:802::2004]

Here is a graph I uploaded to Google Drive.

Prior to this issue in the last week the connection has always been excellent. Now its borderline unusable. I work from home for Cox and that is also becoming a struggle.