poor gas mileage and slow acceleration on 2003 Toyota Solara

My car is getting horrible gas milage and and accelerating poorly. It seems like when at highway speeds the rpms are high like the car needs to shift and it wont. recently replaced a flex pipe/exhaust gasket which dobbs diagnosed without help

Asked by for the 2003 Toyota Solara
suggest letting a Toyota specialist check the car over,
especially if the check engine light is on.