MAC OS 10.7.4 Wi-Fi Problems

I install the new Lion on my 27-inch Mid 2012 desktop Mac and have been having perpetual issues with the WiFi dropping. I have tried all the fixes I could find and none seem to work.
One item suggested it could be modem – but it appears to be new (802.11n). Working with a strong signal – and it has no problems with my Mac Air running the same OS.
Help! This is so frustrating. I can go to the network diagnostics and bring it back each time but I have to do this 10 – 15 times a day.
