It is hard to say what might be wrong here.
Is it ordinary browsing that slows or downloads? or both?
What about ping times (ping
www.cnn.com) to the web servers? Do they increase during your session?
If you run
ifconfig. Does it show a lot of bad/dropped packets?
Are the DNS query times increasing?
dig www.cnn.com
How about the rest of the program, do they run smothly?