I'm working on my coworker's 2004 Silverado 5.3L. Long story short, it is a mess lol. His brother in law changed the fuel pump for him (massive rust hole in the top of the pump) and also worked on the PCV valve. Well, long story short, the pump leaks around the tank seal (I think I see the cause, working on that), he ripped the non-replaceable PCV valve out of the cover and somehow swapped it, and now the truck runs like utter crap. It has codes P0300 and P0135. Pulled the plugs and they're all way past due and very worn, and driver side plugs were jet black. Put new 41-110 plugs in it, fired it up, and it ran great! For a little bit, then started sputting and back to throwing misfires all over. Pulled plugs again, and all the driver side plugs are covered in black soot. Brought up Torque and bank 1 sensor 1 is barely wobbling around at 0.1v. Bank 2 sensor 1 is very lazy. OK, so I'm going to go ahead and swap both upstream sensors (wish me luck lol). But, is there anything else anyone can think of that could lead to just one bank fouling out the plugs so bad?