Ah, come on guys. I was enjoying the thread. Not to highjack it, but, I have the same symptoms, but I'm not ready to post questions until I'm ready to crawl under the truck to diagnose and follow up on all the good suggestions so far. Loose/cracked flex plate, bad u-joints, on and on. I suspect it is my tranny getting ready to take a dump. I have no faith in my Auto E4od tranny and waiting for the day it breaks so I can replace it with a ZF5. It only does the vibrating on rainy days. PO broke electrical connector when changing trans. Tranny acts funny when driving on wet roads. Anybody on the East Coast (a day's drive from DC) willing to do the tranny swap for me.