Help w/ Vibration Problem

I have an 2007 Peterbilt 387, when I start from stop, and go either forward or in reverse, the truck shakes back and forth really hard. It happens as I am easing off the clutch. It does it only when start from a dead stop. I checked all of the engine mounts and cab mounts. Also, I checked the carrier bearing, and it was good as well. Any ideas, on what the issue could be? Thanks.