Try pinging your router (Applications/Utilities/Network Utility). If you get packet loss between the two, there's some kind of incompatibility between the router and your MBP, maybe hardware related.
I had a similar issue where my iMac would operate at 1/3 the speed of two other Macs and two PCs. Switching the Netgear router to an AEBS fixed it.
I had a similar issue where my iMac would operate at 1/3 the speed of two other Macs and two PCs. Switching the Netgear router to an AEBS fixed it.