Your 99 Sport has no power after 50 mph or on freeway but runs fine up to 45 or 50 mph just had new distributor cap wires rotor and air filter please help?

i would suggest checking your fuel pressure. I just had a similier problem with my 98 tj and i replaced the cap, rotor, plugs, wires, up and downstream o2 sensors, and fuel pump. i still had a problem so i plugged in an odb2 sensor and i pulled codes for injector misfire. So what i ended up doing was replaced the o rings on all 6 injectors and bought a can of 50.00 fuel injector cleaner.... my jeep now runs fine... needless to say i spent about 500.00 dollars on parts i really didnt need.