Power loss ocassionally

Hello, I own the vehicle listed above (gen.2 since 2003-2009). I don't know is it linked problem, but sometimes car can't start up from first time and other days starts normally. Alternator charging is 13.4V on idle, but it keeps draining battery to 40%. But the real problem is that car with 150kW sometimes act like it has only 50kW. One day it drives like crazy and the other it lacks of power. Sometimes even in the same trip it lose power and gain it again during ride. No dashboard warning lights or codes. I changed spark plugs, vacuum pipes, clean throttle body and MAF sensor. Charge battery to 100%. Engine, transmission, differential oil and filters changed. When it has no power, I noticed louder sound like engine struggles, lower fuel economy, harder or unable to reach 180kmh and next day it just works fine. Lot quieter, faster, better fuel economy, easily reaching 180kmh and great throttle response. What should I replace or fix to enjoy ride again?