I'm really not understanding this..

My truck has a SLIGHT vibration when driving between 2-7MPH it feels like the timing is off and the idle is rough. Its almost like I'm driving on a very rough surface like pebbles

But the thing that throws me off is when I'm completely stopped it don't vibrate.. when I'm simply rolling forward at that speed with a SLIGHT amount of pressure on the gas it don't vibrate.. when driving at higher speeds it don't vibrate..

I'm confused!!!

Nothing under the truck looks abnormal either.

 

My truck does the same thing along with clunking on the downshift while braking.

I just found this on search so im kind of late.

Its when you barely are on it rolling forward and at about 800-900rpms it starts to virbrate.

Is it a driveline problem or an enigine problem?