What state are you in that's gotta be awful loud... your local highway patrol gonna be okay with that volume?
To answer your questions, yes slipons/mufflers do affect both power and torque on these motors. And yes, if you intend to keep that "slip on", I'd definitely remap it.
Did your bike have the dual high mount/under seat mufflers standard? If so, the ECU mapping is radically different to what will be required for your current set up.
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