Weird shaking when sitting

I'm sure that this has been answered before, but just keep getting lost in all the posts/searches. I've got an '03 X with the 3.3(Non SC) Auto trans. When i'm sitting in Park/Neutral everything is pretty good. When I shift into any Drive Gear D/R/1/2, I get a very noticable vibration. It really only does it when I sit still, or maybe I just don't notice it as much while moving. Also, It seems a little lacking in the power department.

It's got a fresh-ish oil change(about 700mi ago),and I just replaced the distributor cap+rotor(Bosch), spark plugs(NGK Iridiums), and the plug wires(NGK). I did it all myself so I know that it all got changed right, i've heard stories about mechanics slackin' on the #6 plug.

Took it up to Advance to have the codes pulled, P3028(the knock sensor) is the only thing that came up. Could that be the only thing that I have going on? Any input would be great! Thanks!