Ok is this a long bed truck? Does it have a carrier or driveshaft support bearing? Have you had the tires checked for balance? Have you rotated the tires to see if the vibration moves with it?
Now on you multi cyl. Missfire, you have an engine light on? Is it giving code P0300? I would like you to check the cap and rotor first as this disign of cap does have a problem also how old is the fuel filter? Do you have a digital multi meter? Get back to me with what you can and we will go from there.
Tuesday, February 16th, 2010 AT 8:57 AM