I'm with Sixto on the cat being possibly plugged. After you did a purge did you take the car out and run it hard? It may well be plugged. remove the plug on the front of the exhaust manifold (made for pressure checking the exhaust line) and see if it runs better.
If so then you may want to do a Cat-ectomy!
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!