First of check gear changing. Is it changing gears correctly? Could happen a faulty transmission and you are always driving in 2 or 3 gear.
Check transmission (notice rpm while driving on low pedal).
Second, check fuel pump pressure and petrol injectors. Petrol must come on specific pressure and injectors holes must not exceed specific Dia, and extra petrol must return in reverse pipe.
Third, check idle rpm, smoke to gues possible ignition fault.
Fourth, check rear tires for possible jam in break drum. The car with Jammed break leathers don't feel much in driving but costs extra effort to engine.
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