MR6500 - Rooted, cannot execute AT commands

[axkwireless]

I have a MR6500 that I was able to run AT commands on and switch my telnet port to 23.
However, I have lost access to port 5510 and now when I telnet in, I only have root access. I have scoured the internet for like hours trying to figure this out but I just can't seem to find anything.

I can't for the life of me figure out how to run AT commands under root. I tried running ADB SHELL to no avail, and AT, getting "Not Found" message every single time.

I'm looking to add some bands maybe, and have the ability to run more AT commands, but it seems I am sort of locked out. I don't really want to reflash firmware and go through the process again if I don't have to. Any tips or advice?