New advanced router, slower speeds

I signed up for Verizons new advanced router, I went from the FIOS router with one antenna to the new one with 2 antenna so I could have better WiFi coverage in my house.

Before hooking up the new router, did a quick speed check on my PC and was getting about 11 mbps over WiFi.  Hooked up the new router and it dropped to 5 mbps.

Wired my PC to the new router and it went to nearly 50 mbps (where it should be). I downloaded verizons optimization tools and that was no help.

Plugged in my old router and it returned to 11-12 mbps.  One more time to the new "advanced" router and back down to 5.

Any help on why my speeds are so much worse with what is supposed to be better technology?

Thanks!