2250 low rail pressure code

[loghauler]

One of my drivers was headed to work empty this morning. Called and said the service engine light would come on for 5-10 seconds, derate engine, and then go off and return to normal. It happened 5 times in a 50 mile span. Got him to stop at friends shop, plugged up and the last stored code was fuel rail pressure. Replaced fuel filter on frame (truck is a kw with paccar filter housing). Code didn't pop up again until last load this afternoon, and it only popped up while loaded and truck was in a decent pull. It happened 7 times this time, and again lasted 5-10 seconds and went back off. He's empty now and it hasn't done it anymore. Fuel pressure is 158 on each side of filter base. Any ideas? Truck was serviced this passed weekend with all new filters. TIA