If you're looking to break into narrating audiobooks for the major publishers, then character voices, effects, et cetera, aren't the only thing you need to worry about.
I've been doing post-production, editing, and mastering on audiobooks for most of the major publishers (Simon and Schuster, Harper, Random House, etc) for the past ten years. The industry has shifted from where producers mostly decided on whether your voice was right for the project, to where whether your voice is right AND the quality/level of your own post-production.
Over the years, I've had to tell producers that, despite the fact that someone has a good voice, the amount of editing that's needed to get them to a quality ready for distribution, doesn't make much financial sense and they've been dropped.
So, what I think is important for your reel and ongoing projects, is to show that you can deliver audio not only without any mistakes (re-reads, long pauses), but also breaths, clicks, mic pops, etc and mastered well. In other words: to be able to deliver distribution-ready audio.
That I can definitely help with.
If you send me your showcase material, I'll edit and master it to reflect what I deliver to the producers and publishers I work with, which is then sent to Audible and other channels for distribution.
If you're still interested, send me a private message, and I'll cut some audio from my recent projects to show you what I have done.