Drivetrain hesitation starting out

[cropdust]

I've got 2003 dually with six speed. Last 1000 miles starting out from 1- 5 miles per hour I have a hesitation in my drivetrain like something is slipping. It has only happened about 10 times. It has done it with the truck only at 1000rpms, never done it with a 15000# load. I've started out hard trying to get it to slip, but doesn't do it. Any suggestions where to look. If it would do it all the time I would put it in 4 wheel drive to help the process of elimination.

Is it possible the clutch could be slipping and then grabbing occassionally. I'm running Power Pup on tow mode.