I have an 08 chevy Impala Ltz.... When I use my AC lately the service stabiltrak/engine power loss warning comes on the dash. It also starts shifting extremely hard. I know these are 2 different things so its rather confusing.

 

running the ac puts more load on the engine, what are the codes?

 

That is all it says... Service stable track and then says engine power loss. It throws a engine code of P0420 but its done that since i got the car. This new problem just started here recently.