I've tried it all but still slow internet

Question

I've been suffering from very slow connection speeds for months now. At first I thought it was my DSL ISP so I switch to Comcast HSI and it's a little faster but still nowhere near acceptable. I just got off the line with Apple support and I was stunned by the lack of imformation I received! My Apple Care subscription was a total waste of money. So I'm hoping someone here has a nugget of wisdom that will help me out.
Here's what I know:
HSI line out of modem is good. Plugging a PC into the same modem and cable gets 7mbps download speeds. My dual 1.8 G5 running 10.4.3 gets around 850kbps with the same cable and modem.
Problem exists whether I use Airport or ethernet. I am currently using ethernet to the modem to keep things simple.
I've zeroed out the drive and reinstalled the OS. (not fun)
I've trashed all caches.
I've tried with and without DNS addresses in the network preferences.
Flushed Safari and reset Safari.
Firefox and Explorer get the same slow speeds.
Logging in as new test user gets same speeds.
Tried lookupd -flushcache in terminal
Tried with and without Broadband Optimizer
Ran Onyx
Ran Disk Warrior
ipv6 on or off no difference. Currently off.
All proxys are off
Reset modem, unplugged all cables, zapped PRAM, unplugged and replugged a thousand times.
Repaired permissions at every update.
There is more but I can't remember them all...
I'm hoping this rings a bell with someone and they remember how they solved it. I love Apple and I've been Mac-Only since around 1998 but I'm really disappointed with their support performance today.
Any help will be appreciated.
David

Answer 1

Yes that is indeed slow and inline with your previous testing.
Couple things, you have dual 10/100/1000 ethernet ports in that computer right? I am not familiar with the insides yet to know if they are built-in's or if they are on an expansion card.
It is not likely that the PC laptop and your Mac are using the same brand of ethernet chips so there is an avenue for testing. Nor is it likely he may also have had gigabit ethernet capable ports.
The cable-modem wouldn't likely be a gigabit ethernet equipped unit but its worth checking its specs.
What I would want to do is three fold.
1. The ethernet ports on devices are usually auto-sensing for speed. However problems do occur in networks with some devices not playing well together in the sandbox so we have to force one or more of the devices to use a specific speed and what the call a duplex setting.
If for sake of an example that comcast modem only had a 10 megabit/second half-duplex port for you to plug in, if your computer was through auto-sensing goof-up talking 100 megabit at full-duplex duplex or 1000 megabit at full-duplex ethernet or even 10 megabit at full-duplex to that device you have communication error. At the correct speed but wrong duplex setting you can end up with framing errors and late collisions with devices.
2. You have dual network ports most likely on your computer. It would be worth a test to see if you can disable/shut one of them down and let the OS only have to handle the one.
3. If you have a plug in expansion card with ethernet on it, it would be worth a test if the two you have are built-ins and still not working. Also, and much easier would be to see if a friend or work has another Mac you can use for one day as a test to see if it works. If it does, that pinpoints it to something specifically unique about your computer, not the OS, still perhaps a setting in the OS, but I would focus more on the hardware differences (your network controllers). If you use the same cables and it works on the other Mac then you've eliminated that as well.
Hopefully lots of new ideas to ponder.
I also have some commands you can type in that can speed up your maximum throughput on the internet but while they can give you another 100-200KB/sec on downloads, we need a working base connection.
Jan J.