Q: Wifi only works after PRAM reset and then only until sleep

MacBook Pro 15'' (late-2011), 2.4 Ghz, 16GB memory, OSX 10.9.4 (Mavericks) everything up to date.

After waking from sleep, the WiFi does not recognize any networks, or even an internet connection. The wifi icon is either completely gray or an empty white quarter-circle. Wifi can't be turned on in Network Preferences (nothing happens). The only solution I have found (on these forums) is to delete the wifi connection, hit apply, shut down the computer, restart while holding Alt+Cmd+P+R (PRAM reset). Then the wifi will work flawlessly until the computer goes back into sleep - which happens any time I step away from it.

It doesn't seem like a hardware issue because I can get it to work fine with a restart. However, I can't find the software setting that will fix this.

Thanks for any help.