I have two OUYAs and installed GP on both. I had similar problems on one of the cubes, but it turned out that it was just a misconfiguration.
Did you make sure that the a-little-hard-to-see-checkbox in the Xposed installer?
In contrast to the common instructions availabe e.g. on YouTube, I turned SU & Mods preserver OFF in the Mod Collection.
After that, GP worked with no problems.