Some segments are slow
It is unclear why some segments are quite fast and others quite slow. With a static number of total segments, your download will not finish until the slowest segment is in. Why doesn’t the app maintain the same number of active segments, creating new segments on the go after old (fastest) ones finish, in order to speed up the download further? Algorithmically this should be straightforward.
BoronBone about Download Shuttle: Speed Boost