Plugs, coils, very possibly a stretched chain, if the chain is stretched that bad and it's skipped a tooth you may have bent valves!!
Also look out for a vac leak if you've recently removed the manifold!
Currently having the same issue with my 2010 VE V6 omega, timing chain was recently done about a year ago now so I’m pretty sure that’s not the issue, I’m currently in the process of replacing all 6 spark plugs and coil’s also camshaft sensor. will let you know if there’s any change. Than if you like give it ago yourself and see if that helps with the problem.