I experience this as well, but only after the car has been parked for several hours in the parking garage near my office. Dealer said they "couldn't duplicate the problem" so I shouldn't worry about it. I'm worried about it.
Same thing (or similar) happened to me the other day. Started the WK2 (V6) and felt a slight jump almost like it wanted to shut off but turned back on in a split second...like it missed. This happened right after I hand washed my Jeep. Maybe someting got wet while rinsing the heck out of it?
What a waste of time, the dearler had my the truck for two days and can not fine the problem with the bumping, they told me they made some adjustment to the transmission but the bump on start up is still there.