rough running, no codes being read on 2001 Chevrolet Lumina

Car starts easily, idles well. When put under power after warming up (2500-3000 RPM) it starts cutting out. Code reader will not pick up any codes, even if a spark plug wire is removed.

You may need a scan tool instead of a code reader to find the cause of your problem. It sounds like you are describing an engine misfire. If that is the case the check engine light should be flashing while the misfire is present and fault code(s) should be set. With no codes stored the next step would be to monitor the data from the engine control module using a scan tool in order to try and see if any data parameters are out of range or try and determine which cylinder(s) is misfiring. Have you checked for a restricted catalytic converter?