I will look into ForScan. The ICP voltages I listed above - are they readings to the computer from the sensors, or readings being applied to the controllers from the computer? Obviously the ICP pressure reading is a number calculated and displayed by the computer, not the actual pressure it's seeing. I'm stuck at the moment on the fact that the truck runs the same whether the ICP sensor is plugged in or not. That's great information about the pump I'm familiar with them - it sounds very much like what I'm experiencing except the the pump (according to the numbers and by the way it sounds and feels) can supply 1700 psi at 1/2 throttle, but not if I move the throttle past 1/2. That logically seems more like a safety feature. My plan right now is to replace the ICP sensor and see if that changes how the truck drives, as well as pulling the ICV to see what it looks like at the screen. I can do those cost effectively and without tearing into the top of the motor - I would replace it anyway if I do replace the pump.You need to be looking at the voltage reading from the sensors, the PCM will use internal numbers if the signal from the sensor is unreliable or out of parameter -- the voltage reading will always be accurate
Yours is an Axial Piston pump, it uses a rotating valve plate, that is subject to scoring -- when this happens the plates can separate under higher pressure, and come back together when the pressure lowers. I think this may what you are describing.
The other problem with tilting the truck making a difference in starting, may have todo with the HPOP leaking oil from the reservoir (worn pump shaft or seals) this leak will drain the reservoir over a few hours. The low pressure pump will refill it, but takes some cranking.
ScanGauge is an OK monitor, but falls short on reading codes -- look at ForScan, I have posted several times about it being the goto tool for these trucks