Did you leave the stock naturally aspirated exhaust on there, or any other parts? IIRC, the naturally aspirated exhaust is 1.5" diameter which would pretty severely restrict the TD. The OEM 1.6lTD exhaust diameter at 1.75" diameter is still very restrictive, but would be much less so. Are there any other differences you are aware of your setup different from a factory TD setup?
Are you seeing full boost pressure, which should be 9-10psi? Is there any smoking under wide open throttle? Lack of boost and/or lack of fuel could cause low power output. As could mechanical problems, like poorly spraying fuel injectors, a badly timed fuel injection pump, or perhaps partially melted piston tops or other internal damage. A poorly timed fuel injection pump can also drastically effect power, but is relatively easy to fix.
When was the last time you changed your air filter?
PS - Is the red dyno plot a plot of another 1.6lTD engine that is running better? Dyno results aren't always 100% accurate by the way. It is recommended to do 2 or more tests if there are any questions, and make sure the results repeat.
Also, make sure the dyno operator depresses the accelerator pedal 100% during the test and that the input lever on the fuel injection pump hits the stop. Good luck!