2006 E500 4-Matic brake pedal very firm

Its also not easy to stop smoothly, as it just feels like I'm not able to modulate them the way I want. Also, there's a pulsation, but my brake pads are still very meaty. I have new rotors and pads in the box ready to install, but I want to fix the hard pedal issue first.
I work at an independent mechanic shop, and we don't specialize in Mercedes, but we have an expensive snap-on scanner. What should I look for to try to understand what's going on?
Thank you!




