Red triangle, limp mode, P2122, P2138, B2271, C1378

Well, it turns out you were right, it wasn't the gas pedal. Having driven about 500 miles without any problems, I got the red triangle with the same symptoms yesterday.

I didn't have my Techstream with me, and needed to make it home, so disconnected the battery for a few minutes and was able to make it home.

So now it's either an ECM or a wiring problem.

 

In case somebody stumbles upon this thread wondering if there was a conclusion. It looks like there was. It seems when I originally took out the hybrid ecu, then put it back again, I didn't connect the harness properly. It seems to be working fine now. Another shout out to @ChapmanF, he was right yet again.