Your Tahoe, my 2000 Yukon Denali, like all the 96-98 pickup trucks, '99 SUV's (technically the 5.0 & 5.7 were used till 02 in the vans) those half ton vortec engines suffer from an exhaust flange that warps, blows out the gasket and set a bank 2 downstream O2 sensor code. That's because the downstream O2 sensor is mounted AFTER that friggen flange
Check the flange for an exhaust leak before replacing any parts. If it is indeed blown out and warped, replace the gasket. If it doesnt seal, and blows out again, theres a company called REMFLEX. Their gasket material will crush, conform to the uneven metal, and rebound to seal when its heated for the first time.
I tried to sand it smooth, double gasket, high heat muffler cement, you name it, to get it to seal. Wasnt until my fat fingers typed away on the ole internets and found REMFLEX. And I'll reccomended it to anyone that needs it.