Elberg

Hey guys. I bought a Skoda Octavia 2019 150 hp 1.5 tsi a couple months ago thats driven 136.000km and quickly after felt a loss of power when accelerating hard. Had it to a tuner a week ago to get a stage 1 tune to see if it helped. We put it on a rolling field before the tune, and it showed 132 HP and 232 nm only (should have 250nm from factory). We tuned it and it went up to 150 HP and 269nm, but he said the tune should give 180 HP and 320nm. The acceleration is alot smoother now tho.. He tried to diagnostig the issue of the power loss with a tester, and told me to buy new NGK spark plugs because it showed alot of errors from the cylinders, and said that would probably fix it and bring it to 320 ish nm. I changed them yesterday, but still dont feel the change. The airfilter looks good too. My question is - does the engine just lose that much power over time, can it be something else I need to look for, or is it just because its showing WHP on the rolling field? Thanks beforehand.