[speedlever]

Surely your dealer's shop put an OEM axle on there, right? If 3rd party, I've seen reports of that causing similar issues.

 

[speedlever]

You are dealing with multiple mods on your suspension when you have both a lift and the 20's installed.

Do you have hub-centering rings for your 20's?

I'd be curious to know if your issue is resolved by going back to the original 245/65R17 tires and wheels.

Edit: do you have a 2007 or a 2009 RT? Your profiles says one thing and your text in the OP says another.

 

[speedlever]

Put your stock wheels back on. That will eliminate one variable. If it fixes it, you know where to focus your attention.

If you don't have hub centric rings with your 20s, that could well be the source of your vibration.

Read here:
http://www.ridgelineownersclub.com/forums/showthread.php?t=36394
http://www.ridgelineownersclub.com/forums/showthread.php?t=40495