Loose pipe question...

I have a pro circuit on my 91 kdx and recently all but one of the rubber mounts holding the pipe in place came loose. The rubber separated from the metal backing plates.
I took them off and removed the screws in the rubber and drilled holes all the way through the rubber and put screws all the way through the plates and hangers and just tightened everything back up.
The pipe is nice and tight now.....but....the kdx does not seem to rev as high at WOT and does not produce as much power as it did before I hard mounted the pipe......what is going on????? any ideas??

Well I figured it out today....it wasn't the pipe that was robbing performance....it was my sparkplug that was unscrewed all the way to the last couple of threads! JUst about to fall out!
Tightened that back up and she ran great!