How to get rid of my lag when i play ps3?

ok, so i have a wired pc that is upstairs. i have modem and a linksys router sending the signal to the basement where i play my ps3. my ps3 usually gets around 90 to 100% signal strength. my internet provider is verizon and we pay for 3mgps. i just used a internet speed tester and im getting about 2.5 mgps on the pc. when i am downstairs in the basement sometimes i will get really good connection, but lately i have been getting really laggy slow internet through my ps3. the router is only 2 years old or so. my ping is usually around 47 if that matters. any ideas how to fix this???? there is no possible way for me to run a ethernet cable from my basement to the top level of my house just fyi. any help would be GREATLY appreciated