Hello, my name is XXXXX XXXXX I will try help you with this.
Can you tell me the year and current mileage.
Has the timing belt ever been changed?
The first thing to check is with a scan tool to see if any faults have been recorded. You can also look at the live data to see if all the sensors are reporting valid readings.
For instance if the long term fuel trim was high then this is an indicator for your fuel consumption figure.
Next would be a mechanical check of the engine. Check the engine compressions for each cylinder. See if any are lower that the others or if they are lower than expected.
You should also have the brakes checked, a binding brake could cause higher consumption.
If the revs are limited to 3500 rpm in every gear then that needs to be investigated. If it is only in top gear then that could be just because it is an under powered engine.