Gain horsepower by increasing airflow, and reducing exhaust back pressure. For more airflow install an after market air filter, or a complete cold air intake system. To reduce exhaust back pressure, install a free flow designed muffler.
For more fuel and performance consider installing a programmer of your choice.
with a basic radiator flush, you could help prevent water pump failure, thermostat failure, and sludge build-up in your radiator and radiator hoses...which in turn could help prevent your engine from overheating.