Certain sites run slow, but fine under different user account

OK, I have a wierd one here. There are a few sites that I go to where things load really, really slow. I have a program called DUMeter where I watch the upload/download speed of my connection, and these sites come across to me slowly, maybe 1/3 to 1/5 the speed of 'normal' sites. The one I am having the most trouble with is Auctiva.com. Things time out, I get messages that 'a script on this site is causing IE to run slowly, do you want to stop running it?', uploads to the site run slow or fail, etc. Another trouble site is my eCommerce site, where I try to bring up large HTML editing windows (like 1600 lines of HTML code). Maybe I have issues with other sites, just not as bad or noticeable?

HOWEVER, I get the exact same behavior from FireFox AND Google Chrome. Stranger still, if I log in under a different user name on the same computer, everything runs fine on those sites and the transfer speed (again according to DUMeter) is normal. These pages load in 7 - 10 seconds, as opposed to maybe a minute or more under my normal log in. I can also access these sites quickly and trouble-free from another PC on my network, through a switch and the same router. It also runs XP Pro and IE8. Both fully patched and up to date.

So I have tried the usual suspects - clean boot, defrag, clear history/temp files (Google Chrome was downloaded only as a troubleshooting measure for this issue, and had no history at all - yet has the same symptoms right out of the gate), disable NAV, disable Windows Firewall, IE add-ins (even though all 3 browsers do the same thing), cleaned out all my Java history/temp files.

Using the other login is not a viable alternative for a million reasons, other than troubleshooting. For comparison, I am on DSL and load USAToday in about 5 seconds under both logins, with any browser.

Why would these sites alone behave so strange? This is a fairly new install of XP ( a few months).

 

I have thought about that a lot and gone to great lengths to try and detect anything out of place. Of course I run all MS updates, IE is set to medium high security, up-to-date NAV w/ intrusion prevention and e-mail scanning, AdAware checks once per week. I have also run Hijack This and posted to other forums (happy to post it here if anyone wants to look at it) and nothing seems to come up. I have also run Process Explorer to look for any wierd stuff, but everything seems to be legit. I have also manually run the MS Malicious Software Removal Tool, direct from their site with no trouble and MS Windows defender. I have come across nothing that indicates any malware.

It just seems odd that these 2 sites give me fits with IE, FireFox and Google Chrome but everything else seems to work just fine.

One thing that has happened to me is for a while my online banking site thought I was connecting from a cell phone (you get the little 40x60? pixel version of the site) but when I called they said one other had called about the same issue. After a few days it was resolved by them. However, I have also had the same thing happen to me at pizzahut.com and one other site. Is there something on the (my) PC that leads a site to think it is serving a cell phone??

Both sites that I have trouble with have pages that end in aspx, so could this be a server side issue based on something my PC is telling it?