Fascinating thread. I have had my 81 300SD for thirty years and never heard about the 2-1 shifting. I continue to be amazed by the old time MB engineers.

That said - could his problem be the switchover valve?

Also - he might try comparing performance with the AC compressor turned on and then turned off. Not sure if this will tell you anything but I have considerably more oomph off the line when running the AC system in Econ.

Brian - you are a wealth of info.