Try this on the MBP:
* Connect to the 2.4Ghz network
* Hold "Option" and click the wifi icon in the top menu
* Note the "Transmit Rate"
* Repeat this for the 5Ghz network
When I first setup my Time Capsule I noticed that my Mac often times was attaching to the 2.4Ghz network. At that point I separated the networks and did the above.
Low and behold, each time the Mac picked the 2.4Ghz network it did so because it had a higher transmit rate than the 5Ghz one in a given location.