If the one leg of the "Solenoid Fuel Pressure" and of the "Solenoid Fuel Quantity Solenoid" are "Pulse Width Modulation" as WWDiesel states then you need to place an Oscilloscope there to see what is going on! Using a Digital Meter there is meaningless!
So looking at wiring Diagram 8W-30-14 these "control " wires would appear to be the Brown wire from C1 Pin 52 and the Brown/Yellow Stripe wire from C1 pin 76.
You could try spraying some Contact Cleaner on these contacts at the ECM and the C1 Connector...the contacts on the connector and the ECM are very delicate....the Dealers use an Extender Block fitted between the Connector and the ECM so as to be able to get their instruments into those positions without damaging the contacts.
You can try unplugging the C1 connector...with battery disconnected.....and measure with your Ohm meter from the pins at the two relevant solenoids to ground....should be no continuity to ground if the C1 plug is disconnected!
Make sure you are not holding the leads of your meter with your bare hands while doing these measurements!
When I do measurements on wires like this with a meter I tape a sharp pin or needle onto my meter leads and piece the insulation of the wires themselves...you can close up any holes in the insulation afterwards with some glue or melt the insulation.
This way you can check for shorts to ground and for continuity from end to end!
These Sensors themselves may be faulty if the failure only shows up at Freeway Speeds!
Check the ECM Ground is clean and tight...the Black/Dark Green wires going to G100 as shown on the diagram.