the negative on the wide band is it reads an average of BOTH sides, you have an issue on one side. not sure if that is going to tell you anything.

I would tighten the intake botls/do kuehls test. reading the plugs IS helpful, it has shown you that you have an issue.
take a look at the new plugs now, check intake and exhaust bolts. exhaust bolts can make it lean also due to no back pressure. then just drive it and keep an eye on it.

perhaps due a comp and leak down as a reference/check of the engine.

you could even swap injectors or send them off and have them cleaned.
if you don't want to do that then put in a bottle of techron with a half tank of gas and go drive the piss out of it. I don't drive hard, I just try to keep the RPMs hi, like 4-5k range. just hold it there if you are in traffic or between lights, that gets the injectors flowing more fuel. then put a bottle in with a full tank and drive it normally. then check the plugs again,.

you cannot be serious???????/ like 4-5k range. just hold it there if you are in traffic or between lights.........????????