07.5 Vmax rough cold start (with video)

[Chewy21]

I have a 2007.5 GMC Sierra 1500 Vmax 6.0 with 195k on it. I've been trying to backyard track down why it's been giving me a rough cold start like I have an aftermarket cam for maybe 5-10 seconds then will work itself out. It will only do it once after I start it after it's been sitting for 8 hours. If I turn on and off right after the rough start, it'll start up just fine or going into the store. 
 

No rough idle at stop lights or outrageous idle. Truck is 100% stock besides the flowmaster cats. Has anyone ran into this before? I can't tell if there's a leak in the fuel lines or maybe the start of a dead lifter? 
 

I've replaced knock sensors, b2s2 02 sensor since I have a p0430 code, new air filter and cleaned the MAF and TB. 
 

 

[CamGTP]

That's a tough one because it doesn't really last a long enough to figure it out. Could be a something valve train/VLOM related but hard to say.

 

You could test fuel pressure key on engine off and then starting to see what it does.

 

I'd also be curious as to what the truck says the current alcohol content of the fuel. Those trucks should use a virtual flex fuel system and they have been known to go wonky in the earlier trucks. They'll read like 30% or 50% even though the fuel is really just regular pump 10%.