These rail pressure code problems come up occasionally during the hotter summer months in trucks with some miles on them - like 75,000 to 150,000 miles, while the injector data (balance rates, etc.) looks just fine when sitting in the dealer's parking lot.

The Bosch high-pressure pump appears to have a more difficult time producing the commanded rail pressure when temps are high and the fuel has thinned due to the high temperatures. Not able to meet the commanded pressure could be due to excessive fuel return flow in the injectors, pumping plungers in the Bosch CP pump not able to produce the pressure or a heat-related problem with the fuel rail pressure sensor.

With higher heat, the close fitting parts within the injectors and pumps can't generate the pressure it needs to. One way to mitigate this problem is to do something to keep fuel temperature down.

Is the return fuel cooler, located ahead of the fuel tank, clean? You can also maintain a higher level of fuel in the tank. More fuel in the tank provides a larger heat soaking reservoir. Worst case scenario - a low fuel tank and a mud caked cooler, then tow heavy in high heat. Is a larger fuel cooler or an auxiliary fuel tank (to keep the main tank full, longer) workable ideas... instead of replacing a set of out-of-warranty injectors?

If this were a 6.5, I'd suggest temporarily raising the fuel viscosity by using motor oil in a 10% mix to help determine whether the problem is due to a worn fuel injection system. Can't do this with a DOC/DPF equipped 2007+ truck. But, what about B5 - B20 bio-diesel, which is approved for the LML?

Jim