I cleared the codes numerous times and it keeps coming up (I have my own OBDII in the glove box with the Haynes manual.) I searched around a bit and noticed all the talk of the spark plugs so I ordered some of the Denso plugs (the OEM double platinum) from sparkplugs.com. If that doesn't fix it I can't think of anything else. When the engine was replaced, so were all the gaskets plus the guy does good work so I suspect all the sensors were thoroughly cleaned. Just pisses me off that I just got my car back with a low mileage engine thrown in and it runs smooth as butter minus the damn CEL constantly flashing.
Thanks for the help guys - this is definitely a solid forum (unlike some others I've tried to use in the past.)
cheers,
James