Your downloads aren't "slow". That's what you get with 56k.

56k/s = 56000bit/s
1byte = 8bit
=> 56000bit/8bit = 7000byte/s or 7kbyte/s

That is the max theoretical speed achieved under laboratory conditions (whatever your internet speed booster said: it is wrong). In practice you get 48000bit/s or 6kbyte/s connections. Therefrom you must subtract the protocol overhead of TCP/IP and Gnutella. What remains is your actual download speed rate (maybe max 5k/s - 5.5k/s). So 4k/s is quite OK...