2012 Cadillac SRX - P0306

What is your question?

I have a 2012 Cadillac SRX, brought it to the shop for a P0306 cylinder 6 misfire. There is also a couple dozen other codes which I assume all communicate on a shared line. - Swapped the spark plugs and coils, replaced 3 fuel injectors (One on 6 and two others were cracked so also replaced), swapped the battery because it died, no change - Checked for voltage, compression, ground, fuel delivery, spark, all looks good. Assuming it just might not be firing at the correct time Shop says the have trouble communicating with the PCM and it also stops misfiring at 3000 RPMs, they cant do PCMs so they gave the keys back to me. Went to go start it and the battery is dead AGAIN, even though parasitic draw is within normal range. I'm assuming it has got to be a short somewhere and may not be the PCM. Something a normal parasitic draw test can't detect, maybe the alternator diode? Any insight helps