I rode a giant for 7 years on a terry falcon saddle.

I recently broke down and bought a cannondale synapse and set the bike up almos identically to the giant. The saddle setback, sadde height is exact. I am getting some chafing on my right ass cheek. (same model saddle I've done 50k on) what could be causing this?
I also have a new set of shoes I have set up with the ergon tp-1 cleat tool. I can figure out what could be causing this. Saddle to bar drop and reach is nearly identIcal.
Help is appreciated.