I have an 2006 FXSTI, nice bike but quite as a mouse and wanted to order the Cycle-Shack Slip on SS. If I redo the muffler what other step are to be done?

 

In some cases just changing the pipes is OK without any other mod. Check with the manufacture and follow their recommendations. If you change the air intake you should re-jet the carb or re-calibrate the EFI to get the mix right. Too lean a mix can damage the engine. This topic is discussed frequently in this forum. Just search around the engine, exhaust topics etc.