"Backfire" and black smoke when starting hard acceleration?

I bought an 18 Camaro SS new, and it's always had this problem. When starting hard acceleration (I don't normally drive it hard), there is a short hesitation after I smash the gas pedal then a sound like a carbureted car backfire, and then black smoke out of the exhaust. It doesn't do this the whole time under hard acceleration; just when first starting the hard acceleration. It seems it has to be an ignition or fuel problem, but it's never thrown a code or displayed a service light and has always passed my area's required emissions test. Car is stock. I had it checked by two Chevy dealers (who likely only plugged it into a computer), a local car repair chain, and a hot rod type shop that dynoed it, and all found nothing. Even though the fuel system shouldn't have been dirty from the factory, I've also run several bottles of in-tank fuel cleaner through it over the years to no effect. I'm not sure if its normal or related, but it's always had a "lumpy" idle - like an old muscle car with either a big cam - or a miss. The hot rod shop says it does have a big cam and thought nothing was wrong with the idle. It runs/drives normally otherwise with no perceptible exhaust smoke. After you let off the gas (not just under hard acceleration), it sometimes has a popping sound in the exhaust, like old manual muscle cars often did. My understanding is that Chevy designed it this way for that sound. Thank you for your time, and I hope you can diagnose this problem.