FTP slowdown at Level 3 company in Broomfield

Good news: For several years our Comcast Business Class automatic FTP backup of changed files on our 50 domains has worked great.

Bad news: For the past few weeks it has been failing at about a 90% rate every night. Multiple tracert tests show a slowdown at Level 3's computers. Repeated calls into Comcast have directed me to call Level 3, and Level 3 people say they can't help since I am not their customer.  

Has anyone else experienced this problem recently?  Does anyone have any suggestions what I might do to get it resolved?

I plan to contact the PUC with my test data if it doesn't get resolved soon, but I'm hoping someone can shed some light on this first. 

C:\Users\John>tracert craigware.com

Tracing route to craigware.com [50.62.106.72]
over a maximum of 30 hops:

1 1 ms 1 ms 1 ms 10.1.10.1
2 14 ms 19 ms 19 ms 96.120.13.65
3 24 ms 18 ms 18 ms xe-9-1-3-sur02.englewood.co.denver.comcast.net [162.151.38.21]
4 22 ms 19 ms 19 ms ae-10-sur03.englewood.co.denver.comcast.net [68.86.104.121]
5 10 ms 18 ms 29 ms GE-7-6-ar01.denver.co.denver.comcast.net [68.86.128.5]
6 1888 ms * * lag-16.ear2.Denver1.Level3.net [4.68.63.165]
7 * * * Request timed out.
8 52 ms 58 ms 48 ms 4.28.83.74
9 69 ms 60 ms 52 ms be38.trmc0215-01.ars.mgmt.phx3.gdg [184.168.0.69]
10 50 ms 68 ms 58 ms be38.trmc0215-01.ars.mgmt.phx3.gdg [184.168.0.69]
11 60 ms 59 ms 59 ms ip-97-74-255-129.ip.secureserver.net [97.74.255.129]
12 83 ms 72 ms 76 ms ip-50-62-106-72.ip.secureserver.net [50.62.106.72]

Trace complete.