98 tahoe engine knocking and multiple codes

I have a 98 Tahoe that I purchased a few months back. total problems so far are losing o/d and today it started knocking bad. its not out of oil and the knock seems to be coming from the bottom of the motor. the codes said bank 2 system too lean,manufacturer controlled fuel and air metering, manufacturer controlled transmission. as well as a misfire.sby my name you should know I have no idea where to start. but the term knock sensor and bearings were talked about when I had a buddy take a look earlier. any ideas or input is greatly appreciated. o yea and sometimes at around 70 MPH it starts to stutter

I have a 98 Tahoe that I purchased a few months back. total problems so far are losing o/d and today it started knocking bad. its not out of oil and the knock seems to be coming from the bottom of the motor. the codes said bank 2 system too lean,manufacturer controlled fuel and air metering, manufacturer controlled transmission. as well as a misfire.sby my name you should know I have no idea where to start. but the term knock sensor and bearings were talked about when I had a buddy take a look earlier. any ideas or input is greatly appreciated. o yea and sometimes at around 70 MPH it starts to stutter

The engine is a 350 (5.7L) correct? How many miles on the engine? Have you or anyone else done any work such as replaceing plugs and wires, distributor cap, etc.? What's the condition of the oil? Very dirty?