I think you doing something wrong reading the DTC. What kind of scanner do you use?
You need to get codes from relevant computers:
(MBDOC - are these the SIX your were talking about)
If you reading of the DM code 6 is correct, it would cause limp mode. This code maybe there because somebody moved throttle control linkage from the engine compartment. If so reset it. I would reset it anyway and see if it came back.
Code 5 is Right EGR (left side of the engine) wouldn't put it in the limp mode (but will turn MIL on). This is most likely not the EGR valve, but the small hole into the intake manifold needs cleaning.
I don't think any other codes have any relevance to your problem.