You didn't say what kind of Chevy you have; so I had to guess and looked up a C1500 pickup with a 5.7. There are 4 oxygen sensors on that vehicle; 2 upstream of the converter, and 2 downstream of the converter.
But what you described does not sound like an oxygen sensor problem. The fact that it is better when accelerating indicates it is a rich fuel mixture problem. A bad oxygen sensor will cause a lean fuel mixture; not a rich one. It sounds more to me like a fuel pressure regulator with a ruptured diaphragm. This is a common issue on this motor; You can check the fuel pressure regulator for a leak by disconnecting the rubber vacuum hose from the regulator when the motor is stopped, and see whether there is any fuel in the hose. If there is any fuel in the hose; replace the fuel pressure regulator.