Is my timing causing me a P0300 code

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Hello everyone.
So a few years (2018) To be exact I pulled my engine after I was trying to add some headers to my engine and it had to many broken bolts.
So I basically refreshed the whole engine added new bearings an LS2 chain and LS7 Lifters and Valve Springs (The Blueys) with a splash of color to make it pop. I added a Melling MTC8 cam. Its a very mild cam it was cheap but I was a novice when so many other brands are out there with much better items for sale.
So for the last 5 years or so I have been chasing down a P0300 code and have thrown the parts canon at this beast because has not been right.
Its a smog year for me and my catalytic light has not turned off and the Pending and Stored code may have something to do with it. I asked some one a tune would help and he right away asked if my timing could be off. The Cam is so mild it should not be behaving this way according to him.
So I looked back at my old pictures of when I rebuilt this engine and if you look closely the sprockets are off by a tiny bit. So I wanted to ask some more talented people on here should I bite the bullet and reopen the front to realign?
Some of the symptoms I can easily describe.
* sometimes the engine runs fine
* sometimes the engine stutters on take off
* sometimes the engine shakes during idle
* Sometimes at full throttle the engine is very bogged down and has no response
* sometimes you can feel a sputter (like a rocking motion) as it its trying to get into another gear
* sometimes it shuts down while in reverse
i was not trying to make a rocket when I rebuilt this engine but it's not like before.
The Truck operates great over all
Oil Pressure is over 50psi at all times
The fuel economy is back ( I can drive from LA to Sacramento (450+) in one tank (21 gallons) in fact it might be better than when new.

The Engine was an LM7 it has 280K when rebuilt
and now has about 304K since the rebuild.
Items I have changed after the rebuild trying to chase my tail
- new Spark Plugs (broke some of them changing the manifolds)
- new wires (autozone lifetime warranty)
- new coils (not OEM)
- rebuilt injectors
- new MAF
- intake air pressure sensor

So what do you guys think, i need to perform open heart surgery on her again?
 

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Fernando Escobar
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all aftermarket cams need the p0300 code deleted as the lope you hear is actually misfires. so they will misfire at idle and throw that code. part of the cam game. seems like you need it tuned. timing marks look ok to me.
thanks I hope this is what it needs its getting very inconsistent and I need to pass smog already
 
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Fernando Escobar
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The One thing I never checked because of my inexperience then was push rod length, I have the tool now and the fact I had to use different heads and ls7 lifters I should probably check them in the near future. good thing the heads don't need to come off for this
 

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