o2 sensors/check engine light

my light came on my 94 tbird and i ran the test and it said my o2 sensors where running too rich so i replaced both o2 sensors and now it runs like it has no power at all (when i barely give it gas)and the light still comes on even though i cleared it with the ecc machine. i re-did the test and it said o2 sensors where running low people said i needed to brake them in (o2 sensors) is that true? and also when i start the car (when its cold) it strugles to turn on and its starts to raddle and sound as if it was caburated not fuel injected then 2 seconds later it goes to normal...does anybody know what i can do. i would really apreciate it