the engine idle control is internal to the ECM programming and is not adjustable via the diagnostic program.
rpm's are preset in the programming, the ecm monitors the rpm's at idle no load and during a load and compensates under load by monitoring vacuum, air & fuel ,ignition timing, and rpm's and attempts to adjust the rpm's when a load is applied to hold the programmed rpm setting.
If your truck is not idling up when hydraulics are applied or steering is applied then you may want to run an air/fuel mix relearn to start with. You could be having problems with the MAF sensor, the throttle body, or fuel system.
I would try cleaning the vaporizer out by removing the drain plug and letting any built up oil residue drain, also use some carb cleaner and remove the air horn from the top of the throttle body and clean out the intake port. Do not attempt to clean the MAF sensor because the cleaner will damage it, if you suspect the sensor being defective it should be replaced. If this is an LPG truck there is the fuel injector that may be dirty, also there is a filter screen inside the fuel port inside the injector body underneath a small cap (held on by 2 screws) that can be cleaned or replaced.
Also using the diagnostic software you can monitor sensors and components while running to see if any other issues might be causing this problem.