I have a 2015 Sierra with an L83 and 6L80 trans. I have not had any luck with the GM 5.3 product as I had one loose oil pressure at 115000 and now this one dropped cylinder 7 at 56000. I am looking to swap out the engine with an l8t using the l83 accessories, wiring harness and ecm. l8t_burb has done this with HP Tuners. I do not see why any tuner cannot do this as it is using the stock ecm and same engine sensors as the L83. I am looking to see if anyone has done this or is willing to help. I am good with an engine but I have not played with GM software.