ok im kinda new here and to the duramax i have a 05 lly with airaid cold air edge with attitude 4 inch turbo back mbrp and egr blocker plate my truck has almost 200000 km on her now and had it almost a year i have a problem maybe someone can help me with here a few months ago i was going down the highway and everything is fine bring her home for the night and in the morning going to work i notice my truck has a strange vibrate to her about 95 to 145 km/h only when it defuels but underload its fine i changed u joints tires re balanced crawled under and check if anything was loose and i cant find nothing there is a very small if any vibrattion in the steering and a more noticeable vibration in the seat and a thunking in the floor boards did this ever happen to anyone im confused about this problem

 

Jack up the ft end and check to see if the wheel bearings are loose. That will cause wierd vibrations.

 

X2 yeah I'd check them out.

 

i check her out and there is no play in the front end at all there is a tinny bit of play in the slip yoke only up and down i asked a few mechanics and said its normal