Downloads start faster, then slow down in a few seconds ?
When downloading files (usually with a web browser), it is completely normal for transfer speeds to appear much higher in the first few seconds.
What happens is, transfers begin early, while you're confirming the download and choosing the location to save downloaded files.
Your browser starts the download (up to the size of RWIN) even before you choose the destination file name, location on your PC, and click ok. That's why transfers appear to be much faster at the beginning, then settle down to a slower, actual rate in a few seconds.
Some residential broadband providers also offer "Powerboost", or "Turbo Boost" technology that offers increased capacity for transferring smaller files (up to 5-10MB). This feature is intended to speed up small file triansfers, while larger transfers would still default back to the user's rated bandwidth cap. In such instances, it may appear that your transfer starts much faster than your rated speed until it settles down to the actual available bandwidth.