I see great RPM swing in lowest gear, maybe the shift points are off? (Adjust bowden cable length between the "throttle" control and tranny). What if you move the gear lever through the motions on your next run, does that help?

In the lowest gear, do you get matching thrust in your backside off the line from dead stop (indicates good ALDA) and renewed life again at 2500+ RPM (when turbo boost comes on)? Do you blow black smoke out the back at any time during the run?

Check the air filter and I'm wondering if you have a constricted cat in the exhaust. Remove the bolt you see or EGR tube from the exhaust manifold and do a re-run. Will be loud don't let that fool ya into thinking you're going faster.

Lift each wheel, in neutral, and spin it to see if you're dragging a brake.

Looks like you're leaking pressure in the turbo cross-over tube to manifold, new gasket.

Oh ya, green coolant is bad for this engine. Zerex G5 or Benz coolant only.

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Cheers!
Scott McPhee

1987 300D