Awasu was never intended to be a hard-core, high-performance podcast downloader and what you are seeing is probably Awasu behaving as designed.
To avoid it going berserk downloading stuff if a lot of things arrive at the same time, Awasu downloads files one at a time. New files go to the end of the queue, so there might be a delay before it gets downloaded. If there's an error (e.g. a timeout or a broken connection - certainly possible if you're downloading a large file), Awasu will re-try an hour later so that might also explain the delay.
If it's critical that enclosures be downloaded as soon as they arrive, it would be possible to write a channel hook script that gets called whenever a new file is found and downloads it, or forwards it on to a third-party download manager. Somebody already wrote something similar to push downloaded files into iTunes
and then his iPod. Not sure if it still works, though...