I'm getting the impression that you are revving the car while in your garage without a load. Yes?
The Crossfire has a programed limit as to unloaded RPMs. I noticed it myself awhile back. My car did not stop running, but it did not want to get much past 2500 RPM. I did not force the issue and try and make it go beyond 2500 RPM. I was doing something in my garage on the car, but I can't remember exactly why I was revving the engine.
I suggest when you have a good RCM and have the Bosch CPS installed, clear all codes and then take the car out for a gentle drive and see how it responds.
A bad CPS will kill the car when out driving, but often after the car cools, it will start and run normally until it gets hot, and then again stop running. So replacing the CPS with a BOSCH will correct that problem. It has been suggested that the connection at the CPS is to blame, but that has not been definitively proven. If you have the CPS out inspect the connector carefully. A new Bosch does fix the initial no run while hot problem. I had the OEM CPS problem years ago and installed a Bosch replacement. That replacement is still in the car ten+ years later with 80,000 miles on it and doing fine.
Most scan tools will not dig down into the manufactures codes. They are OBD II scanners only, so you may be missing some information. The Crossfire has a diagnostic system that is unique unto itself. Getting the correct scan tool is important when digging down to fix some problems. Not knowing what tool you have I suggest reading the Scan tool info here on the website and decide for yourself if you need to, or want to get another scan tool.
Testing for exhaust back pressure is fairly easy.: remove forward O2 sensor and install adapter with PSI gauge. Kits available on ebay, or take it to a shop that works regularly on Mercedes and have them preform the test. Should not cost very much. If you get a kit yourself the pressure should not read above 3 PSI if all is well.

PS I took that heat shield off that is just to the rear of the CPS as it makes it much more difficult when servicing the CPS to have it there in the way. I ground the bolt down a little so it wasn't quite so long then screwed it back in it's hole.