the diffrence between 2-d and 3-d response of a RC frame

[greatFAZ]

Hi every body.I modeled a 2-d RC frame both on 3-d and 2-d space,and i plotted the pushover but the responses are different.especially the basic deformations(chord rotations) are different.i think i've modeled both of them correctly,because they have have almost the same frequencies and periods.i used the rigid diaphragm for this frame on 3-d space and element truss(rigid) on 2-d space in order to consider the effect of rigid diaphragm. note that the frequencies of frame on 2-d space is exactly the same with SAP2000,whereas the periods and frequencies of frame on 3-d space is a little different(about 3%).i wonder why the responses are different?which one is correct?PLEASE HELP ME!!!!!!!!!
regards