Line Speed Drops..

[#1]

Can some one please tell me why my Line speed keep droping after hour and thirty minutes to two hours?
when i connect my net it shows 448/6944kbps to /5900kbps and drops to 2000kbps.. when i reconnect i get my speed back but its annoying 

[#2]

What is the make and model of your router? Could you get hold of another one to try?