Im working on a 2018 Atlas and have been chasing a weird miss. started on cylinder 1, swapped plugs and coils with no luck. then swapped injectors with no luck. Scoped intake and found lots of buildup on cylinder 1 valves. Compression test showed good compression on all cylinders but running compression test showed 90 on 2-6 and 50 lbs on 1. Given that no other issues were found and these vr6 engines are known to have build up issues we removed the head and sent off to be rebuilt and machined. Head came back looking great valves were all cleaned up and lapped and the ports were all cleaned up real nice. got everything back together and started it up only to now have a cylinder 4 misfire. went through the same process, checked plugs coils scoped for anything weird or stuck in the cylinder, even swapped that injector as well. still nothing showing an issue. again did a running compression test and found that every cylinder except 4 is at a healthy 90lbs while cylinder 4 is at 70. basically back to square 1 just in a different cylinder. totally baffled on this one, any advice?