f there is more than about 10 seconds between transfers, when I try to upload another file FileZilla goes through the whole connection stage again (Resolving IP address, Connectiong to ...), which takes at least 10 seconds.
If Filezilla times out its connection when you are transferring files, try disabling the Timeout setting.
To do this, click on "Edit" then choose settings. It will bring up a window like this:
Change the Timeout to zero as shown, click OK, and you're ready.