Welcome To TD!!!
Unfortunately I cannot help you with the DRB issue and I do not have any wiring or specs for your D250 but...
The systems all operate the same way so what exactly are the issues with this truck that you need/want to diagnose?
Somebody here may have the info you need.
In the meantime if this is a cranks but will not start or other driveabilty issue...
First thing you want to do is be absolutely sure the...
1)Battery is Good and Fully Charged.
2)Spark Plugs are not Fuel Fouled.
3)There are no stored fault codes.
If the battery has been disconnected or went dead crank the engine 7-10 seconds then check for any fault codes.
4)If there are no stored fault codes then before you start digging into the computer control systems be sure all of your basics are correct.
1)Engine Mechanical(Compression, Cam Timing,yes its a chain)
2)Ignition System(minimum of 25 KV at each plug, plugs are not worn/fouled)
3)Fuel System(Fuel Pressure, Quality of Fuel if the vehicle has been sitting)
5)Vacuum System and Vacuum to Map Sensor.
6)Air Intake or Exhaust Restrictions
Sensor specs such as the Map/TPS should be the same as the 2.2L/2.5L/3.0L engines.
CHECKING MAP CALIBRATION
1)Backprobe the Signal and Signal Return Lines at the TPS connector with a digital voltmeter.
2)At closed throttle voltage should read .30-.90 volts.
(If closed throttle voltage is above 2.50 volts the controller will think the engine is flooded and will shut down the injectors)
3)Slowly sweep the throttle open watching voltage, it should rise steadily and consistently with no voltage drops or spikes.
4)WOT voltage needs to be above 3.50 volts.