2000 4x4 Blazer Question

During Summer I replaced plugs, rotor and cap. Also all 4 brakes and rotors for my daughter. Blazer has about 90k miles. Daughter is telling me the gas mileage has dropped in her car about 4-5 miles loss in mpgs. Also during the summer she had it at a friends gas station and he noticed that one side exhaust gasket is leaking and the exhaust is a bit loud with a cold start. Would this exhaust leak cause the drop in gas mileage? Going to have it fixed in next 2 weeks.

thanks

Any exhaust leak before the oxygen sensors will cause the sensors to indicate a lean mixture. The ECM will richen the fuel mixture resulting in a loss of fuel economy and engine performance.