updated from 50 Mbps to 75 but only the Up speed has improved; speed down is the same

[tr8881]

When I do speed tests, they are consistently  ~ 49 Mbps down and 39Mbps up.   The down speed hasn't improved at all. That's where it was with the 50 Mbps service.

 I've run the FIOS optimizer on my PC (as administrator).  

 When I run Verizon Network Diagnostics it discovers a 45 Mbps T3 link.   How can a 45Mbps T3 deliver 75Mbps speeds?