I just wanted to make sure that the pressure gauge is NOT supposed to move unless the truck is cranked. Mine will go up to 75 lbs when I turn the key on. Any idea?

 

Yup, your sending unit is failing. Cummins has a part that is a direct replacement at a mere $85, rather than the $200+ they want at the auto parts store. PN is 4921511

Your gauge will shortly start dropping out while driving down the road. This causes the PCM to scream about looking at the guages.

Procedure to replace the sending unit is a bit crazy. Its best reached by hand from underneath to unclip the wiring, and from the wheel well with a 4' extension and swivel to actually remove it. Installation can start by hand from underneath the truck, then use the extension to tighten it up.