The car is 11 years old with almost 200K mileage if the meter has not been reversed. other then the 3 speed automatic transmission limit. as I told the the guy above you the O2 sensors wear out & effect the milage as well. the guy with the mini pajero 660cc 3AT fixed his average by changing the fuel injectors my point is 200K is a high mileage even if the engine is in a good condition there are other things that have a life span & simply wear out n in the OBD scanner might seem fine & don't give any error codes an example being O2 sensors & fuel injectors. Fuel filter of this car has never been replaced before isn't available locally & kabli one is of no use and needs to be bought from an importer costs around 20K
The thing is in Pakistan people will say ''agar koi issue or masala nahi day raha hain to replace maat karo'' & will often hear the terms like ''kuch nahi hotah hain'' same people don't bother changing gear oil , brake fluid , coolant of their cars & use tap water in the battery instead of distilled water. use Guard filters
So I think doing the following things underneath will surely improve the average
A swap of the transmission & ECU with 4 speed one
New O2 sensors
New Fuel filter
& changing fuel injectors