Detroit 60 series hard start in morning

Hello all. Having a strange problem with my truck and I was hoping someone here would have a clue based on my particular symptoms. I have a 2005 Freightliner with a 14l EGR Detroit 60 Series. For the last several weeks if I turn the truck off for several hours I will have to crank the engine over by holding the ignition key to the start position for little bit arnd 1 min before she'll start to slowly crank over but then she'll idle and drive just fine. By this time I get a low voltage warning since I'm really drawing on the batteries. I was told by a few different shops that it might be a bad fuel check valve thats allowing diesel to run back down to the tank.
Have changed FCV also put new injector O rings and cups.
Tested new fuel pump and same thing.
Also new check valve on water separator.
Checked fuel lines for leaks and there seems none.
Still doing same hard start in morning. The really weird thing is if its fuel related then how come a few spray shots of Starting fluid on the intake have no effect on starting any sooner?
Anybody has any idea if its related to some electronic.

Looking forward to suggestions as I cant figure out whats wrong and running out of ideas

Will appreciate any help..
Thx

 

It cranks for like a minute before it fires up...after that no problem during the day. But after i park it overnight it has same problem

 

I leave it for minute or so generally but have tried leaving the key on for more than 5 mins too but its always same result