New Intake and Oil change makes a TON of difference

I hadn't cleaned my k&n air filter in like two years so I bought a new cone filter and went to work this morning making a new one. Yesterday I finished up the LS6 intake manifold swap (damn injectors are a pita to rewire) and got everything fired up and hooked up the old intake and it really didn't feel like anything had changed. So today I got the new filter and some silicone and tubing and went to work. Make a very simple tube with 90* 4" silicone elbow and a filter on the end, changed the oil/plugs, and fixed an exhaust leak and now this thing feels like it found 75-100hp. It is night and day different than 3 days ago. Is it possible a simple intake swap can bring the thing back to life that much after the old nasty filter was ditched?

Could have been a combo of issues that attributed to the power gain.