Check your fluid level, though I doubt thats it. Otherwise I'd take it to the dealer. I was having the same problem every once in awhile, it wouldn't downshift into first when coming to a stop and then would pull out in second, but mine would downshift into first if I moved the shifter there. I had it at the dealer and they reflashed the module for me and it seemed to take care of it.
SOLD-08 Unlimited X, "jeep green", auto, limited slip, hushpower muffler, Aerotech Interceptor gauge,Powerstroke tranny cooler, skidrow evap skid, AFE Pro 7 filter, Teraflex leveling kit, EVO control arm skids, 15x8 Black Rock 909's, 33" KM2's