I don't have an answer but would love to hear if anyone has a fix for this. Mine has ALWAYS vibrated at idle, in drive, in warm weather. When I took it to the dealer when it had 25,000 miles, they said "They all do that" and attributed it to the V8. It now has 113,000 miles and is doing it just like it did 6 years ago.
Mine does NOT do this in cool weather. I have a new fuel pressure regulator, new rotors/caps, and spark plugs. New motor mounts helped a little but it's still noticable and annoying.