Check for leaks, my Delkevic 14" Tri Oval (on a 2013 Versys) seems just the opposite, smooth high speed throttle, no engine struggle or clutch issues, engine braking seems much better. Not sure on gas but probably a bit less due to the throttle / sound factor. If anything it does feel more open (a tad less compression) but nothing that causes any disappointment. I took it out on the twisties yesterday for the first time - awesome, the fact that I could really hear the engine in the curves, downshifting and accelerations, IMO made for a better more connected performance on the course. I hope you can remedy the issues with your exhaust.