There are a few factors which could affect the speed of a download.

One is how many other uploads that host is currently serving on at the time you're downloading. The T3 host you're downloading from may have another 20 or 30 hosts it is uploading files to.

Another is the amount of throughput the host has dedicated to uploading files to other hosts. They could be on a T1 or T3, but have turned down their upload throughput to the lowest setting. Combine that with the possibility of a bunch of other uploads occurring at the same time on that same host, and that could lead to some rather slow download speeds.

Then there is the quality of the connection between you and the host you're downloading from. It could be an over-congested router or something at some ISP down the line that could be causing a degrade in transmission speed.

Then there's the possibility that the host you're downloading from really isn't on a T1 or T3 and they've just set it that way in LimeWire in order to increase the number of host connections they can maintain at once. (And as you may know, more connections means more hosts to search for the files they want.)

So, it's quite normal to encounter this.

[EDIT: Just forgot to add... As for your lack of uploads, you might want to make sure that ZoneAlarm allows LimeWire to act as a server. Otherwise, ZA won't allow LimeWire to accept any incoming connections.]