Have issues with codes 1209-1211. 2002 7.3, 210,000 miles 3,000 on oil. Truck starts fine with IPD duty at 12% and around 490-520 PSI. Truck idles and drives fine at low load. When trying to accelerate or climb a grade it falls on its face. IPR duty climbs and sits at 75% while pressure climbs to around 1300# then drops to around 700 PSI. Letting of the accelerator duty drops back to the mid teens while pressure spike up to 3000# +/- for a few seconds then drops back the a “normal” range consistent with duty cycle. Air ways are clear, no smoke to be seen, EGT 800 when loaded, pulled IPR apart and looks like new with no sticking. Im thinking HPOP. Any other ideas?