slow wifi after 10.6.8 update using wnr2000

First time post for a first time Mac owner. I've noticed a significant drop in wifi speed to the point where youtube is not smooth. Using MBPro 7,1 with xfinity blast. Down/Up speeds are 40/6Mbs on ethernet but 3/4Mbs on wifi. As far as I can recall, the only changes ive made are updates to Mac OS X10.6.8 (is this Snow Leopard?) and Parallels for running Windows. Please Help