Bank 1 sensor 1 code help
 

I have a P2A00(bank 1 sensor 1) code sofar ive changed both bank 1 sensors, all new exhaust gaskets headers,pre and post cats, and new maf sensors and still have the code any ideas on what it could be?
Not sure if its related but now my gas gauge is malfunctioning. Also i had the code cleared and it stayed off for about easy 120miles where i never rev'ed past 4k then immediately came on when i got on the throttle. So im thinking its a fuel delivery issue. Clogging injectors, filter, or failing pump? Still no other issues besides the cel.