Part of your problem is probably turbo spool-up. These turbo engines need to be above 2000 or so RPM to begin making their power. If not, they'll go, but they will be slow. It may be your typical driving habits (if youre very light footed) coming back to get you.

Also, check that your transmission isnt shifting too early. Do a search on 'bowden cable' to see how to change your shift points. If you screw it out, the trans will hold gears longer. I have a problem where my shiftpoints are too close together, and sometimes are really low, so Ill be in 4th gear by 20-25 mph. If Im not hard on the throttle the car will be a slug at that point, especially if going up an onramp.

But my car has plenty of power under 30 mph, so long as Im not expecting v-8 performance, and keep the right gear.

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
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1996 Dodge Ram CTD (442k)
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Past Diesels:
1983 300D (228K)
1985 300D (233K)