2008 6.7 has been on a diet since 2009 with a shimmed rail plug and never skipped a beat. As of recently i’m getting long crank before it starts whether it is hot or cold. If I hold the throttle at about 25% while cranking, it will start considerably faster than without any added throttle. Is there any kind of a return valve or check valve of some sort on the high-pressure side of the system that could be stuck open or partially stuck open. Brand new fuel filters.

 

Man, that sounds like injectors, I hate to say. Check your oil level, see if it's high, thin, and/or smells like diesel.

If I remember right, the PCM has to see a certain rail pressure before it will let the engine crank. If you have a leaky/cracked injector, it'll take a second before it will fire.