Actually looking for someone in NE PA with MB diesel experience who might be interested in working on the problem. Either w/wo owner help. Or knowledge of MB dealer Leitzinger at State College Pa. Trusted diesel truck mechanic suggested them but with little first hand knowledge. I like working on MB but little time with teenagers. Took car to local MB dealer who took problem from no upper power(happened quickly versus over time) to intermittent by replacing 2 vacuum values and replacing contaminated fuel. He added a note "turbo wastegate line line may be in wrong". You have a port on the intake manifold and a line to diaphragm valve. What can be wrong? Called for more info but mechanic no longer there. Scarely.
Symptoms then what I've done.
In first ride home from dealer for 30 minutes, barely 40mph or 3,500 rpm. Slight sensation of engine "hunting" or slight surging. Then poof, more power, not like before so still missing some upper end power but can now do 50-60mph. Next day back to 40mph, drove for hour, no change. Sat for 2 monthes, back working on it. While driving mostly 40mph with couple minute busts of the 50 -60mph.
Thought I found source when I found dirt in banjo bolt, but no change on test drive. Vac valve on side of injector pump, just below ALDA has 1/2"+ stroke when actuated (sorry but I suck on it). Expect some movement and device to hold vacuum which it did. Loosened ALDA 4 bolt mounts and blew into its line. Could detect some movement but very little. Don't know what to expect but it held air. Vac solenoid in ALDA line works, tested on bench with power source and same vacuum source as stated earlier. At this point I might have done sometime wrong. In the solenoid and vac valve I squirted 3 in 1 oil. If problem is intermittent maybe the component sometimes sticks. So if oil is a bad long term thing then let me know.
Line between intake and exhaust is clear and vac valve appears to be ok. Took control vac line off and plugged but no change in drive test.
Waste gate valve holds air but I could not tell if I moved it or not.
Ran injector purge, changed both fuel filters and air filter before taking car to dealer. Dealer also changed both fuel filters so I'm confident the filters are ok.
Just read good article on adjusting ALDA which I have not done but I'm thinking that kind of tinkering would not be smart. Worried I might be over my head a little and make things worse.
Need to fix engine before worrying about fixing body . . .

Mark W
1983 300SD 225k
1986 250 Ford plow truck
1995 Bonneville
2004 Forrester Subaru
1980 Piper Warrior II, 180mph in a dive.