03 z71 vibration and 4x4 issue

[yanahmean]

Hey guys im new here but I came across this site through google looking for a cause for my vibration... I habe a 03 z71 ext cab silverado.. 170xxx miles .. thought my vibration was solely tire related but after putting on my new tires.. (33's) from what was on it (255/75/16) some of my vibration is gone but it still hums at slower speeds but right at 75+ it vibrates pretty roigh almost like metal on metal... also the bigger tires has caused CEL to come on and is saying my 4x4 is jacked and my speed signal in left is jacked so any input on that would be great too.. back to the vibration.. did both rear wheel bearings. Have changed rear diff fluid twice .. drivers side spider gear is pretty worn down and a good bit of play in the rear but I am the 3rd owner and the truck did not do this when I got 17k miles ago..I am getting ready to change the u joints and the slip yoke any other options if that doesn't work??