I have an intel iMac with a Cox connection; the same thing happened to me. (Except I dropped from 5+mbs to ~1 mb) the cables are all fine and the router is fine as well. I've experienced this a lot?connection speeds drop as time goes on. What's the issue?
I have a laptop that suddenly dropped DSL connect speed from an average of 2500 to taking 3-4 minutes to load a site. It is a Toshiba satellite that is about one year old. I reformatted with no improvement.
I contacted Toshiba and took the laptop to an authorized service center and they could not find a problem and did nothing. I had the same problem when I tried to connect.
BTW, I have been online for several years and am not at a tech support level user, but certainly not a novice and have been able to troubleshoot most issues over the years.
I have sent the laptop to Toshiba 4 times and they replaced the motherboard, the LAN card and each time said it passed all benchmark tests and connected at appropriate speeds. Each time I got it back I experienced the same problem with connecting. I spoke to two different Toshiba technicians and they both assured me the problem was corrected
I have another laptop, my wife has a desktop and my son has a laptop and they all connect to the DSL wireless at 2000-2500 speeds. I even gave the laptop to my son and he had the same problem. I have tried several locations and with a cat 5 as wall as wireless.
A few days ago I took the laptop[ back to the same service center as before and they say it connects at the same speed as all of their other machines and can't find any thing wrong with it. I am going to pick it up shortly.
Does anyone have suggestions about troubleshooting this issue? Thanks for any help.