06 silverado v-6

[oomag12]

Local Mechanic welded in new cat. converter and installed upstream sensor..........still had engine light and power loss..... his hand held diagnostic tool then had the same code as before(catalytic efficiantcy bank 2) he than suggested a tune up, wires, plugs, cap, button....same code, loss of power, rotten gas milage. He tells me the downstream sensor is fine, but after the above parts list and labor he's begining to get a little deep in the pocket. This truck was produced at chevy's mexican facility, and I have had several issue's with this truck. It has right at 78000. Just curious if anyone has had simular issue's with v-6's in this model, any info I could pass on to my tech, i would appricate it.