My bike has been very boggy with little to no power in the higher rpms. 5th gear has zero power at all. It idles great but doesn't want to blast off. Current jetting is 370 main with stock pilot, motor is stock except for some mystery pipe, air box lid off. Any help would be appreciated.

Check the power valve and make sure it is closing at high . 

Does the engine sputter at high RPM?

Does the muffler have a spark arrestor incorporated into it?