I missed my Oxygen sensors shipment

[rotarex]

i forgot to mention my apartment on the form, which the form didn't ask for it, so it came to canada and went back to the states, so far i did about 15,000 kms and when 1 sensor went i was getting 550 kms per tank now im getting 450 kms WOW

when i 1st got the truck i got 650 and i think the sensor was cleaned, i know alot of people says it cant happen, but i know its possible, also the nut is stripped from passenger rear side, so im hoping that when i change all 4 with new plugs i get 700+ kms

i hope im not carbon build up