Vuze make use of several types of algorithms to make an optimal use of your bandwidth (Downloads and unload). this feature is called the Auto-Speed selector.
You can configure Vuze to make use of this feature only when seeding files, here's how:
- Open Vuze in Advanced Mode.
- Click on the Tools Menu > Options > Transfer > Auto- Speed
- In the right pane check the box next to "Enable when only seeding"
- Click on the Apply button