And at least on the CAPS era ISL370(Now flashed to 400) (Basically early 2004 models and on, have the Variable Geometry Turbo (VGT) ISL and Common Rail). The Pressure is really basically a Yes/No sensor. On Silver Leaf, it does not vary. On the analog gauge, especially at first start up before the engine has warmed up, you will see higher pressure indicated. But one up to temperature, at least as far as Silver Leaf repots, it's a constant...
Could be different in newer ISL's. (And I know what I was trying to say, and not positive I said it well enough to get the info across - sorry