Any Codes showing in the Display at anytime?
Can try doing a Throttle valve closed learning and see if that helps:

OPERATION PROCEDURE FOR THROTTLE VALVE CLOSED
POSITION LEARNING
1. Turn ignition switch ON → OFF. (And hold it for approximately 5
seconds after turning it OFF.)
2. Make sure that throttle valve operates. (Check for operating
sound.)
3. Upon completion of the above, learning is complete.

Can check your fuel PSI at the Regualtor and see what it is running at,maybe the regualtor has tar build up in it,can drain it: let the truck warm up to operating temperature and then shut the fuel off and let the truck die,on the bottom of the rerualtor is a 12 mm hex plug take this out and let the tar drain then reinstall plug.
To check the fuel PSI(which should run around 4.5 PSI) on top of the regulator is a 17mm hex with a phillips head slot in it,take this out and put a pressure guage in it(a 1/8 NPT will work but dont force it in,just hand snug it) start the truck and see what the pressure is at idle and at full PRM,it shouldnt drop when the hydraulics are operated.