So I was helping a friend do suspension on his car when I decided to take my muffler off and see what was causing the rattle I hear when idling. Apparently it's inside of the muffler. Well now I'm probably just gonna get the tips put on some pipes and leave the muffler off. But to the actual question. Is it normal for the car to shift strangely after doing this. It's hard to explain it's just like you can't even really tell it's shifting. It's an automatic btw. 08 S coupe

 

No connection between muffler and transmission.

 

You got an 08. How many miles? Maybe the trans is going. I think you may just be imagining it since you have a louder exhaust with the muffler off.

 

Placebo effect...kind of

 

I experienced the same thing when I replaced the stock exhaust with a free flowing 2.5 inch cat back. The free flowing exhaust causes the engine to make more torque than the trans is expecting at low rpm and low throttle settings . So the trans will have slippy shifts at low throttle settings. A tune that adjusts the torque output maps will cure the problem and firm up the shifts.