Have you read the other threads about external/WAN drops?
Questions 1 = Have you replaced your modem with a newer, less than 2 year old model from your ISP? This has fixed all of my problems and others as well
If your answer is no, I strongly suggest it, and I would place money on the fault being your modem. DOCSIS V1.0 will not work, DOCSIS 2.0 are sketchy, only DOCSIS 3.0 are solid