Just bought a g37 sedan automatic and it was as driving fine for about an hour and then it started cutting power very aggressively when giving it any kind of hard throttle. If you baby it, it shifts fine and nothing seems wrong. But even barley barley barley stepping on it and it’ll cut, then have power for 1 second, then cut, power….etc. only CEL is for a bad catalytic converter (which is audibly bad). Is my trans bad? Slipping?

 

I’m sure it is your cat putting it into limp mode. I went into limp mode for an exhaust leak when I had my new exhaust put on but just not fully clamped down because it had to come back off for another service so we didn’t tighten it down all the way. Seems like these cars are very sensitive.