Clean out the banjo bolt on the back of the intake manifold. It controls the ALDA system.....a fuel enrichment system (think accelerator pump on a carburetor on a gas engine) that allows for more fuel when boost comes on. If it is plugged, cleaning it will allow as much improvement as the valve adjustment and the purge both. Air up your tires to proper pressure. Just a little down can sap the mighty 124 horse diesel you've chosen. You might try and pull a boost reading. Bet you are not much over 7 to 8 pounds. You can remedy this by adjusting boost on the supercharger waste gate or you can put an adjustment valve in the boost line that runs to the waste gate. If you can get up to 12 to 13 pounds of boost, that will surely help.

Regards

Run-em
1983 300 SD - aka - SPARKY THE DIESEL-