hmm...difficult w/o actually doing the touchy feely thing. I'm assuming you didn't have any vibration @ speed with the stock rims? Also assuming the tires are new (no cupping, feathering) and bearings/ball joints are okay.
I see the spacers are hub-centric on your axles, but how are they on the wheel side? Tight? No play? Mounting surfaces completely clean? Can u check run-out with a gauge?
The other thing might be wheel balance. Not just normal balance, but also weighting towards the edge & towards the middle of the rim. Maybe the shear force from the spacer is amplifying a vibration you didn't notice before? Have u tried a high speed balance with the wheel/tire on the HL? Maybe see if u can find a good tire shop that's worked with spacers before..good luck...
if the spacer/wheel contact is a bit wobbly, you may be able to shim the space with some brass stock to tighten it up and see if it works...kinda labour intensive though...are u shure you're gonna rub without the spacers?