I found Low mileage Issues in My Toyota Belta 1.3 2006

AOA all members

Recently I have purchased a swapped engine 2006 Toyota Belta 1.3 2szfe with CVT transmission. But the issue I am facing that the mileage of my car is reduced at a very low range. The car is giving 9 Km/L with very soft foot within the Lahore city. And with normal foot, it gives less than 8. The condition of engine is fine and not creating sounds o r has no oil consumption issue. Overall, the engine is working properly. I also scanned and thought to replace the o2 sensor and changed it with B1S2. But the issue still persists. Fuel Trim values are within mark as LTFT 0% and STFT -1.56 to 1.56% at idle speed. And during drive at aprox 1500rpm values increased.

A have also done these action but the mileage of my car is still same.

1 Changed Engine oil to Koyama 5W 30.
2 Cleaned injectors afterwards changed them.
3 Cleaned MAF sensor and afterwards replaced it.
4 Got cleaned Catalytic converter.
5 Replaced O2 sensor 2 post Cat
6 Set tyre pressure to 30 psi.

I am working in the industrial electronics as an electrical engineer. I purchased an Elm327/Bluetooth OBDii scanner for my DIY and made a screen capture video during drive with selected display values of Engine RPM, O2S1, O2S2, LTFT and STFT. Actually I wanted to attach the video here but I can’t. I can provide a link of the video here after uploading on YouTube. I think about the sensor values and still have doubt about it my 02 sensor values are O2S1 oscillating From 0.1 to 0.8 but approx 80% it remain in rich values and 20% in Lean. 02S2 is behaving oddly on start it's value rise slowly from 0 to 0.8 but most of time its not oscillating and keep values above 0.6 V but in deceleration it rapidly go to 0V. I have replaced the sensors three times with 3 times and still the results not changed. My friend also has same car, and when I compared these values with his car, the values were same but the mileage of his car was about 14km/l. I am not getting the right direction to fix this issue. Please help me to resolve the issue to get rid of this crucial situation. Kindly tell me the reason why is this actually happening as well.

Previously, the owner of my car installed 185/65 R15 tyres, as oversized tyres are also a big reason to reduce mileage but I searched on Google and I found it can affect 1 to 2 Km/l but not this much.

The pickup of my car is very good. And it can run 0km to 60km/h quickly. But I also have a doubt the CVT gear of my car jerks when I drive the car at a very slow speed below below 20 Km/h and gear seems slipping in the full throttle.