I have a 2006 Silberado Special Edition, and it seems to vibrate at highway speeds. However, the vibration seems to surge in that it comes and goes at a regular interval say every second or so in a rythmic way.

I dont feel it in the steering wheel, but I feel it in the floorboards. My mind may be playing tricks on me but it feels like the truck surges with the same rythym, but it could be my mind.

Its more of a pain in the butt than anything, but Id like to diagnose the problem is there is one. Anyone have any ideas?

 

The first thing I would have checked are the tires. Go have a high speed balance done. I bent wheel or out of balance tire can cause that.

 

I would check out the Ujoints for binding. I would lean towards this to it being rythmic.

 

Sounds like the drive shaft. Maybe the u joints are bad or the shaft may need to be balanced out at a transmission shop. Mine did that too when I installed new u joints. The easiest way to tell is when you feel it vibrate at cruising speeds, give it throttle but not enough to downshift. Just let it pull strong in overdrive. If it goes away then Im pretty sure its the drive shaft.