Interesting...are you still having issues?
It seems your Router was replaced but this actually got worse? I do wonder sometimes if they re-use returned equipment and it also turns out to be defective.. If this isn't an electrical or signal noise issue, or a wiring issue, i'd say your second Router's tuner (modem) is defective! Could also be caused by a faulty filter or splitter, water ingress, corrosion etc..
What's the condition of the co-ax line coming to your property? Is it externally visible?
Those power level readings were very strange indeed!
Please keep us posted!
Regards,
Lee