2000 Nissan Maxima runs rough after warming up. What is the most likely culprit? Have ruled out spark plugs and 02 sensors so far.?

Nissan's are known for bad coils.Areyou getting misfire codesset?

Fuel injectors can also cause a motor to run poorly when they get dirty.

A vacuum leak is also on the list.

If you don't have NGK or Denso spark plugs in the motor throw out what you do have and by those brands.

Found the culprit. It was in fact an ignition coil pack that was grounding to the engine.

I had a 1995 Maxima SE 5-speed and eventually replace 4 injectors one at a time (2 under warranty and 2 not). When an injector went out it was difficult to start and idled rough, but it was not hardly noticeable on the highway. And in 3 of the 4 cases I noticed that for weeks before the check engine light came on. They thought it was due to alcohol in the fuel. But other than that I had it for 18 years with the only non-routine repairs being sensors. It pulled as strong as ever and still had the original clutch.

But I thought they may have sorted that out by 2000. I bought a used 2001 Pathfinder with 99,000 miles on it in 2004, owned it until late 2015 and never had any injector or any other engine/transmission issues at all. It just suddenly had major weak brakes after a panic stop, seized front caliper, cracked rear drum, bad master cylinder, bad rear proportioning valve, some failed pollution control, and 3 broken springs. So I traded it for a 2008 Subaru Outback that still looked like new with 150,000 miles on it.