Perform 3D versus SAP2000 Pushover Analysis

[melaniecho]

I built and ran a pushover analysis on a 2D EBF frame in both Perform and SAP2000. The pushover curve (capacity curve) in both programs are similar, so I feel confident that my model is more or less correct. My issue comes when I try to plot by demand curve. It seems that SAP and Perform are giving drastically different demand curves, whether I am using the ATC40 method, the FEMA 440 Linearization method, or the FEMA 356 Coefficient Method. Has anyone had this problem before? If so, do you know what the solution is, or what I am possibly doing wrong?

Thanks.