I have a 1998 chevy silverado z/71 4x4.
I had a water leak and had the intake manifold gaskets replaced. Ever since then, the check engine light comes on and it soots up the o2 sensors and the 4 plugs on the right bank. It may run good for a month or so and then it starts all over again.
And you continue to accept this a “normal.”
Why?
Take it back to whoever replaced the intake manifold gaskets and ask them to correct their work.