Engine running lean – Kia Forte 2.0 2010

Hi
I recently bought a Kia Forte 2010 2.0. 30 minutes after driving off from the seller, the check engine light came on.
Code P2191: Lean at higher load bank 1.
I replaced the upper O2 sensor, the map sensor and the PCV valve.
I took a look at the sparkplugs, and they were all a little white.
I have also tried looking for vacuum leaks, by holding a hand to the throttle body, which killed the engine – therefore I suspect no vacuum leaks?
The engine does not misfire, it starts right up and runs smoothly – the only signs of it running lean is the lack of power and the CEL.

If I get directly on to the highway within 10 miles, the CEL will not come on.
If I drive around town for 10-15 miles it comes on, when the engine gets warm.
If it is already warm and i drive around town the CEL will not come on.

Maybe you can help determine what the cause could be?

Best regards the frustrated amateur mechanic

Brand: Kia
Model: Forte
Year: 2010
Engine: 2.0