There are 2 possibilities here ether your firewall is only allowing limited connections or your ISP is shaping filtering your connection. LimeWire has no problems if you have a good connection with nothing blocking it. I have no problem DL at 700KBs+ along with many others who use LimeWire. My suggestion is call your ISP and ask what their policy is on P2P apps try a couple of different P2P programs and see if you can get better results with them. If your results are the same with them then you know it is your ISP or your router. And if your router/modem is not configured properly it can have a big effect on your ability to download.
You might find the link below it is about ISP that are know to block otr filter P2P apps and Verizon is mentioned in there but I did not see where it was confirmed. ISP's known to BLOCK or Filter p2p or specifically Limewire