Gen V L83 swap question, start and stall

[GreyGhost85]

Hey guys,
I have a question for you all. I have a gen V l83 swap with 6l80e that I having start stall issues with. However, if I disconnect negative terminal for 10 minutes or so, and reconnect it can run fine for hours. Am I not doing something correctly? I had the ecm programmed through speartech and it was remarkable turnaround time.

1. If I unplug negative cable for 5-10 minutes, it starts and runs perfectly. If I start and run it the next day without disconnecting negative terminal, it starts and fires up just fine, but does after about 15-20 seconds as if something is not registering right.

2. All grounds are tight and clean, all connections are tight and clamped. I added additional engine to ground straps and on body as well.
3. Fuel pressure is solid 75 psi. Walboro 255 pump.
4 . o2 sensors both registering voltage.
5. When stable rpm is about 650, after second start it will stall around this rpm.
6. It will start like nothing is wrong every time it does this.

Any ideas? I will try reaching out to speartech as well to see.
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[LH Lead-Foot]

I think that I would talking to Speartech, if they reprogrammed your PCM. My GM eSI (Electronic Service Information) only goes to 2004. My guess is that the pass-lock was not disabled. With an actual schematic or year of donor vehicle, I would be completely in the dark. It is called removing VATs.
As for disconnecting the negative battery cable and runs fine, no clue as everything in the donor vehicle to the PCM uses EEPROMS which do not change or lose memory by disconnecting power. So?
I ran my 2003 5.3L Tahoe engine on a stand for days cleaning injectors, compression test, etc. Just powered up the BCM, placed it on the class 2 network and bypassed VATs with an 8k ohm resistor at the BCM VATS input doing a relearn with my TECH-II
ASE Master Tech since 78 - Retired