Question is if you were in my situation...mention it or no?
In my opinion, that's really hard to advise at this stage (for someone who doesn't advise against it, across the board, and I definitely don't). I mention it in my queries, because when agents ask what happened with my former agent (and they do), I'm able to respond truthfully about why we parted and it's all fine and reasonable.
Until you actually part with your agent, it's impossible to know what your end result is going to look like. Maybe it will be helpful to include, maybe it won't. This feels very cart before the horse. I strongly advise you to track down your current agent and have a serious conversation.
New agents will not look kindly on a client who queried them before they'd left their previous representation. What would inspire them to trust that you won't do the same to them while they're trying to shop your book? Your agent's lack of communication will no longer be the point, your behavior will.
It's a big decision. I really, really advise you to try to talk to your agent first. Make sure he hasn't been sick, or experiencing computer malfunctions. The signs don't look great, but still.