new iMac: Why does my internet speed randomly slow down or freeze?

Actaully, step one would be me going to the store and buying a 20 foot enet cable so the iMac could reach the cable modem from the desk... 😁 I only have crossover cables on hand right now.

In the meantime, I noticed that I've had perfect access speeds for the past hour, but on a whim tried clicking the + tab on Safari - the favorite sites came up quickly, and clicking on one site made it load quickly, but immediately after that my access slowed to a crawl across all my browsers.

I put a 5e cable between the iMac and the router, turned off Wifi... and the performance is as bad or worse. Pages take so long to load that they routinely time out. Logging in here took a couple of minutes, and the first try Safari reported that the server wasn't responding. Reloading an eBay page that I've had open for a few days (watching a vehicle auction) mean a spinning blue circle in the Firefox tab, maybe the page text loads, and I don't get any images. Or it times out.

Meanwhile, my trusty but definitely EOL Macbook Pro 1.83 sits on the floor, loading every page I throw at it, working over Wifi or a direct connection.

IPv6 is on automatic, with no configuration info established, same as the MBP. MTU on the enet connection is at 1500, same as the MBP.

Thanks for the link, but none of that applied in this situation. I've spent a couple of hours with two techs at Apple since my post, and every test they've put this machine through seems to rule out any kind of user setting.

While we were doing the testing, it seemed like the slowdowns spread and increased in severity, at least as long as I had the machine on the wired connection.The slowdowns seem worse on graphics heavy web pages, though I noticed that certain emails had trouble loading images. Mail.app crashed twice- one if those times it was loading the confirmation email Apple sent me to announce that they would be calling me back soon.

At this point it appears to be a hardware problem, with a system-level bit of corruption being a possible secondary cause. I'll be bringing it to one of my Apple Stores next weekend. I'm disappointed but not giving up. I'm as interested in solving this as the Apple techs are.

An update...

I was supposed to bring my iMac in for a checkup this weekend but I've put it off for a little while. One of the techs asked me if I had installed any software over the stock Mountain Lion install. I read off the list of things I've installed, which was basically updated version of my browser collection, some games running in Dosbox, and some drafting software. Nothing that touched the system.

Then after I got off the phone I remembered that I was working on a Java recompile which you can read about in this thread:

In order to do a recompile of the Java program I was working with, I was told I'd need MacPorts, so I tried installing that. After several lengthy downloads, and an astonishingly long install time, I ended up with a ton of new software that did nothing to help my project. I abandoned it and moved on.

I remembered the long install and I became worried that something in the Mac Ports install may have altered or corrupted my system software, so I decided to uninstall it. One problem - no uninstaller. So I Spotlight'd anything related to the install and deleted it all by hand. A few files were not able to be deleted, because they were "in use". The only programs I had open were Mail, Safari, and Firefox. I closed all those and I was able to finish deleting the software.

Since then, the slowdowns have been much rarer and of shorter duration. Still not perfect. I had a TV show on download while I started this post, and it ran for 1Mb/sec+ for most of the time I've been sitting here, but when I opened a 2nd Safari window to go to my discussion history, it broke again and my download speeds went to zero. Now its back and forth but still working.

At this point it happens enough to bug me but its rare enough that I will probably not be able to make it happen at the Apple Store.

Well, the problem is back, and worse than ever before. It started a couple days ago, and its so bad now that clicking on a single link usually means I get to look at a blank page for at least 30 seconds before it starts to load, just a few elements at a time. I have to wait about 60 seconds for a simple page load.

Its looking more and more like I have a corrupted operating system, or worse, a defective piece of hardware.

John,

I did find out what the problem was; it wasn't the iMac, it was the router. For the full story, go here:

https://discussions.apple.com/thread/5026147?answerId=22094098022#22094098022