As long as the transmission isn't banging into gear, the line pressure isn't too high, generally speaking.
Some trucks shift firmer than others, so who's to say one line pressure is the standard, it just depends on what the GM guy felt like that day lol.

GasG is right, you'll never find out the true line pressure by playing with that handheld or file, you'll have to install a pressure gauge to get the exact line pressure, but then again, it's always changing.

Put the servo in and see how it feels.

later,
allen