That's not really much info to go on. Did you do the conversion, and when? You are running a Cat filter but has the filter head been rebuilt? How long ago was the filter changed? Do you have a lift pump? Tuner?
It sounds like fuel starvation but we need some help determining what has been done to the truck to give some suggestions as to what to look at.
2014 Chevy Silverado Duramax LML Crew-cab LTZ, short-bed, 4wd.
Fumoto Drain Valve
Air Lift Loadlifter 5000 Airbags
Kennedy Lift Pump
Sold: 2004 Duramax LB7
2011 3010 Heartland Cyclone HD 35' Toyhauler