hi bro..

looking at your graph..
flat spot 6500~7250...
at 5000~5750 flat spot.
am i right???

no offence your cars tune is pretty average.. still Rich 12.8 at most time..

power drops off after 7250... "you can get more power at top end".
which computer are you using?

also use a compression meter to tell you which piston has dropped compression. usually cracked ring glens/ piston rings will definately have a drop in compression...

however flat spots are not from your mechanical set up but tunes do a big part of it..

sorry not trying to be a car "guru" just giving my opinion (helping a guy out).

Warmest regards