Help! I have a G37x 2011 AWD sedan at 138k miles and the engine light is on, it has a burning smell (not sure if its oil or something else burning), and it also gives me a hard time to accelerate. There are instances where it doesn't want to go past 35-45 mph or 55-65 mph. When I do finally get it to the speed limit i can just tell it was by force. I have tried to go get repairs done but I don't think the problem has actually been identified and I'm ignorant when it comes to the mechanics of a car. I think it's the transmission but I'm not sure and don't wanna replace it if its not the issue

I got my alternator changed a year ago.
I got some sensors replaced in January.

 

So what was it? Sounds like clogged cats.