Can't download

About 2 weeks ago I noticed that I was having trouble accessing web pages – meaning it was taking longer to load them and move between pages. Downloading from them became nearly impossible because it was so slow. Then it got to the point where the download would start but not complete. I re-installed the operating system after doing a re-formatting of the hard drive with system recovery disks. I put the latest version of Firefox on and that didn’t help any. I called Verizon (my ISP) and they said my speed is better than what they currently guatantee for DSL -300kbps. I checked the modem and it shows 3360 kbps d/l and 867 kbps u/l. I have replaced all the cables. I ran a speed test at Speedtest.net and it showed 267 kbsp and 678 kbps. But when I try to d/l a file it is d/l ing at 5 kbps. I thought it might be Firefox so I uninstalled it and am running I/E now. No change. This morning I took the computer up to Best Buy and hooked it up to their system and it worked fine. It only downloaded at 287 kbps but that is better than 5. I can’t figure out what is wrong. Verizon says have good speed, Modem shows good speed, new cables, and computer worked at Best Buy. What else is there to check? HELP. Thanks in advance.

 

Just bumping this up hoping someone can help.