slow browsing in broadband

i h'v a DSL connection it was running very good with fast speed for last 6 moths but now when i start it up for a sometime like 5 to 10 min. it gives actual speed (DSL plan based) but after that it goes slow down. it is always on connection and running on LAN card when i double click on local area connection icon i saw recieving speed and sending speed is increasing automatically without opening any webpage
what is that is that any spyware or what what is resolution pls provide
what to do pls help and one request dont tell me to format my pc

 

Have you tried scanning your pc with antivirusrolleyes

 

every antivirus i have tried with antivirus also