cylinders 3 and 5 running lean

[95GMC]

As the title states I'm having a very perplexing issue on my new 355 tbi build. Idle is somewhat rough and getting some knock retard with very conservative timing and some surging on decel at highway speeds. My main concern right now is that in order to investigate if I was really having detonation, I started pulling plugs on the bank 1 side (easiest access) plus I also noticed the header tubes on cylinder 3 and 5 were discolored like they had been hotter than the rest. What I found was that the plugs on cylinders 1 and 7 were rich/ black which is what I would expect as I'm just starting on tuning and erring on the rich side of things but the plugs on cylinders 3 and 5 were like brand new/ had been slightly hot. The only reason I could think that would possibly cause this was a vacuum leak on these cylinders. I sprayed some starting fluid at the intake gasket area of cylinder 3 and 5 and there was no rpm change to indicate a leak. I also have a cheap smoke machine and smoked the intake and could not find smoke escaping anywhere especially in that cylinder 3/ cylinder 5 area. My last thought was that since I have a dual plane intake the injector feeding the inside cylinders (3 and 5) would also be feeding the outside cylinders on the opposite side (2 and 8) and maybe even though injectors are new flow matched injectors one of them has an issue but the plugs look normal on cylinders 2 and 8. I'm at a total loss, I can't figure out why these 2 cylinders are running lean. Intake is an edelbrock performer carb intake with a tbi adapter (thick 1/2" aluminum adapter) also sprayed starting fluid/ looked for smoke in that area to rule out an issue there. Could this be an issue with the intake itself? I can't figure this one out any thoughts/ help are much appreciated.

[1project2many]

This might be a tough one to figure out. Reading plugs can be an art form so there may be more to the story or a very different story here.

If they are indeed rich, one possiblility might be that the rings or valve seals aren't sealing as well on the cylinders with black plugs. It's also possible you have a leak at the bottom of the intake gasket. This would be tougher to catch with starting fluid. Smoke the PCV side and block the vent then see what exits the plug holes for #3 and #5. If you're seeing black on the body of the plugs on outside cylinders but not inside, it's common for the inside plugs to get hotter than the outside plugs. It's possible there's an issue with coolant flow through those heads as well. Wrong size or missing holes in the head gasket can cause strange issues. Another step for research might be to swap outside and inside plugs. If the dirty plugs clean up it's likely to be lean or heat. If they stay dirty but the clean plugs get black, maybe lean toward oil control.