Play around with the sources and connections limits until it fits your needs (it depends not only on the kind of DSL you have but also on the ISP and other stuff, so don't ask what's best, just try ;-) )
If it's still not working correctly either a) you have TOO many downloads on queue or b) you have too much of your upload bandwidth being used by aMule, so limit the amount of Kb of upload.
There are no other ways to suffer your problem so, if it persists, it's something non-aMule related. sorry :-/
Greetings!