Hi,
if your upload speed is below 10KB/s, then there is a ratio of 1:3 or 1:4 used, i.e. if you upload with 1KB/s you can download with 3KB/s Maximum and if you upload with 9KB/s there's a limit of 36KB/s.
But there's no such forced limit if you upload with 20KB/s, please check Preferences->Connection->Bandwidth Limits for a download limit. Maybe
aMule's just slow.