Cm875ism hard start after long park

[Chamberpains]

Sounds like your fuel system is losing its prime. There is probably an anti drainback valve or check valve somewhere that isn't working properly. I don't know anything about the cm875. Have you gotten on to https://quickserve.cummins.com/info/index.html and registered your engine? Its free. It has all kinds of helpful info directly from the manufacturer of the engine.