Internet is being really sloth-like

Question

Okay, the last few weeks my internet has been totally flip-flop. Sometimes it's lightning fast like Normal, and sometimes it won't even hardly connect, like now. I use a linksys router conneted to a cable modem about 30 feet away, and I have an Airport card in my iMac G5.
I've tried turning off the Airport card, turning it back on, turning off my cable modem, and router, but no effect. It seems totally random when my Internet wants to work and when it doesn't. I don't have another computer to test and use to see if it's just the internet or my computer. I've ran Onyx and done most of the clearings and other stuff it does, I dobut it would work, and it didn't.
Is there anything I can do other then calling my ISP (Cox Cable) because I hate dealing with tech support.
One more odd thing is, even if athe little Connection signal thing at the top right corner says I have a full connection, it's still really, really slow.
Any advice is appreicated.

Answer 1

Since you don't have another computer to test with.
I'd reccomend going to DSLReports and doing the "Line packet loss testing" when you notice your internet connection is acting funky (If you are able to get to it)
If not another option they have is the "Smoke ping", it basically checks your connection by pinging your internet ip every once in a while for 24 hours.
Either of these solutions will tell you if the problem is outside your mac. High packet loss = slow/funky internet.
If you do opt to use this route of investigation make sure to set your router to accepts pings, otherwise the tests wont be helpful.
http://www.dslreports.com/tools
Also, if you are able to get your cable modem stats while the internet is acting funky and when it's fine it would be a great tool to find out what's wrong. Usually this can be found at http://192.168.100.1 depending on the cable modem you have. Poor signal quality will definately cause the problems you describe.