07 Z HR Stumble after gallery gasket job

[cforsyth0]

Hello everyone, this is my first post here at Nicoclub! I've heard great things about this site and the community.
As you can see in the title, I have a 2007 350z. Gallery gaskets went. I replaced them along with the water pump, chain tensioner, and chain guides. After the job, the car runs great. Smoother than it was before. However, I have noticed it has a stumble at about 1100-1500 RPM. Its like a hitch in the motor, where the power cuts and revs fall for a second before it catches up and revs past the stumble. I've tried all three throttle relearns as well as the exhaust valve timing relearn. Though I'm not sure I did any of them right, none seemed to have an effect. Car threw a P1238 ETC code, I unplugged the battery and it hasn't come back in a couple of hours of driving. If anyone has experienced a stumble like this, any guidance would be appreciated. I feel like I'm running in circles chasing this issue down.