lack of power between 40 and 50mph

You are chasing your tail so to speak. P code P0499 is an emission code related to the - NVLD CANISTER VENT VALVE SOLENOID CIRCUIT HIGH. WHEN MONITORED: Engine running. SET CONDITION: The PCM detects a short in the NVLD Canister vent solenoid circuits. I suggest you take the vehicle to your local dealership for diagnosis and repair.