If other apps are OK in terms of bandwidth, have you been reconfiguring some settings regarding conenction and bandwidth of the aMule? Or running some app that could limit apps connections/speed?
My following advice will likely not help, but that is what i would try - try to rename config file if amule create new default one and try if default config. will work):
Quit the app, backup the config directory (cd;ls -la .aMule), if it is listed, then i would make an archive: cd;tar czf .aMule.tgz .aMule/*;ls -la|grep tgz
if you see the archive file and it has reasonable size, it should have been made successfully.
Then i would rename conf file: cd;cd .aMule;mv amule.conf amule.conf_backup
And run the app and see if bandwidth problem is solved.
