And keeping 4 connections up with a modem is too much. Every connection takes 1-2 KByte/sec in, and approx. 1 KByte/sec out. A modem can only take 56 Kbit/sec=7Kbyte/sec in the most optimal case.
I think you'd better keep 3 connections max. In gtk-gnutella 0.91 you can switch 'prefer compressed nodes' on in the advanced preferences. For you as a modem user this is good.

I think the next version of gtk-gnutella will support ultrapeers, which will drop bandwith requirements for modem users significantly.

Hein