Engine misfires, power loss when warm and under load

!998 3.0 Isuzu trooper ciatation. engine rebuilt, new alternator, oil rail preasure switch and thottle body. Starts perfectly from cold and pulls very well until reches normal opperating temperature. when going up hill or excelerating engine develops misfire and loses power. Sometimes when starting from warm it is as if it has run out of deisel and engine fires as if it would when fuel system is being bled. have checked for air in system but surley if air present engine would play up when cold. Any comments gratefully recieved.