Mercedes: 1986 420sel runs well but suddenly has reduced torque, mercedes benz 420sel, number search results

Question
I have a 1986 420sel that has been a very good car and has always had power to spare.  Recently, for no apparent reason, it has had a complete change in performance.  On level ground it seems to accelerate very well up to about 3500 rpms, then fades off as if it has a governor on it.  It also seems to have no torque when clmbing hills.  On grades that it normally goes up at 65 mph in overdrive, it will not exceed 40 mph or 4000 rpms in any gear.  I have changed the plugs, fuel filter, air filter, and run injector cleaner through it with no aparent improvement.  I had my wife step on the accelerator while I held my hand on the tailpime to see if it was clogged, but the exhaust seems to be flowing well.  Do you have any idea where I should look next?  All gauges seem to be in their normal ranges such as temp, oil pressure, etc. and my economy gauge seems normal at normal flat land driving, but I can't even consider passing a slow moving vehicle.

thanks, Bob G.

Answer
This sounds like classic symptom of a bad catalytic converter.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1986 Mercedes Benz 420SEL
Part: Catalytic Converter
 Note:  50 States
After-market" OBD II Catalytic Converters Not Legal for Sale in California 1995 On!     
 
H3000-74199 Catalytic Converter Federal Only IN STOCK $568.17  
  
H3000-49563 Catalytic Converter Federal Only IN STOCK  $532.33  
  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=cata...