2013 Macbook pro with retina--upgraded to OS 10.9.4 and still having wi-fi problems

I recently purchased a Apple factory refurbished 15" Macbook Pro with retina--immediately upgraded to 10.9.3 Maverick OS, and started having wi-fi disconnects. Apple tech service recommended that I upgrade to 10.9.4, and the wi-fi still locks when I use Safari, Chrome, or Firefox. Initially, the browsing is fast and easy, but after a few minutes of use, the wi-fi locks up. Afterwards, I have to disconnect wi-fi, remove the preferred network, and then turn on wi-fi, to get wi-fi to work again.

Is there a better solution?

Thanks