1997 Lincoln Town Car Hesitation at full throttle

I just bought a 1997 Lincoln Town Car Signature Series and I have changed the spark plugs, the wires, the oil, the oil filter, the air filter, and the fuel filter. it runs great at low speeds and with moderate acceleration but as soon as I try to get on the highway or put the pedal to the floor it bogs way down and I actually loose speed. I have grown up around cars and I have never ran into this problem. SOMEONE PLEASE HELP!