DSL-G604T - Slow Browsing But Fast Download Speeds On New Computer Build

I had recently upgraded my computer, which currently looks like this:

CPU: i5 3570
MOBO: Gigabyte GA-Z77M-D3H-MVP
RAM: G.Skill 16GB DDR3 1600MHz
HDD: Seagate ST1000DM003 1TB Barracuda + Seagate 320GB Barracuda
GFX: Sapphire HD4850 512MB Dual Slot Fan
PSU: OCZ StealthXtream 500W
(The bits in bold were the upgraded parts, up from an AMD Athlon64X2 6000+)

For some really strange reason, my web browsing has been ridiculously slow, with the words "Waiting for [website]" always showing up in the bottom corner of Chrome for a good 10-20 seconds before the website loads. This happens to every website I visit, bar Facebook (secret Facebook virus?). It's especially bad on shopping websites such as eBay, taking upwards of a minute to load pages. I have tried Internet Explorer and the same thing is happening.

My downloads, on the other hand, have been unaffected by the upgrade, with download speeds averaging 800KB/s.

If it matters, my current modem/router is a D-LINK DSL-G604T; my other devices work perfectly fine on this modem, with browsing speeds being faster on my 2G iPod Touch than my desktop computer.

I currently use Avira Internet Security 2012 as my anti-virus.

I also use these extensions in Chrome (if it matters):
4chan Plus 2.5.5
Adblock Plus (Beta) 1.2
LastModified 1.1.2
Neater Bookmarks 0.9.4
PhotoZoom for Facebook 1.1208.30.1
Session Buddy 3.0.16
Xmarks Bookmark Sync 1.0.22
Youtube Ratings preview 2.0

I have tried disabling all add-ons and the speed is still the same

In the middle of writing this, I decided to download Firefox, which has improved on my browsing speed somewhat, but still has hiccups here and there (Facebook takes forever to load in Firefox). But having been a Chrome user for a long time, I would like to stick with it.