On the C36 it sounds like the EGR valve is not working or the EGR pipe from the valve to the intake manifold is plugged. The pipe usually plugs at the manifold end. It can be cleaned with some difficulty by removing the intake pipe from the air cleaner, opening the throttle butterfly and poking with a wire or such. Some folks run a speedometer cable through the pipe with a drill. For the upshift delay it is either a problem with the upshift delay solenoid valve (in the double firewall are on the pass side) or the vacuum chamber in the throttle position cable.

On the C280, the only time I've had a communication problem was when the OVP relay was bad. It feeds power to the diagnostic module.