My name is Roger and I will do my best to help you with this.
These two symptoms sound related. The reduction in power can occur when a DPF fault sets. I suspect you may only need a regeneration performed. This cleans out the DPF filter which is collecting the soot. The dealer can perform a regeneration forced using the BMW tester and then it needs to be drive for 45 minutes at highway speeds.
This should only cost a 2-3 hours of diagnosis time to scan, verify the fault, and run the regeneration for you.
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