S4 "slower" then S3

Any reason my S4 would be slower then my S3 over a Wi-Fi connection?  I have 20 MB cable at home and my PCs and S3 all hit about 18 MB transfer rates using Speedtest.net.  My S4 only gets up to 5 MB??  I can run them simultaneously or separate and the result is the same.  Wi-Fi is important since T-Mo has no real 4G in my entire state.