Swapped muffer

[RSTwarmachine]

I recently swapped out the factory muffler and replaced it with a Flowmaster Outlaw race muffler and now the transmission acts up from time to time. It seems like it gets confused on which gear it needs to be in. I left the flapper valve and the baffles. Curious on anyone's thoughts on what's wrong..

 

[PistolsFiring]

Seen other members complain of this issue when running larger tires and no speedometer adjustment, potentially. Not sure how just a muffler swap would cause this.

 

[Izzyduck]

Are you sure it's not your cylinders cutting out, and now your just hearing it more.

 

[Stormin08]

this sounds more legit, you are just able to hear the changes now.