While starting up from a stop lite, my Pacifica started out in 1st gear then it felt like it was in neutral for a few seconds before it jerked back into second gear
How many miles on it? When was the last time you changed or even checked the transmission fluid? Your Pacifica had a 5yr./60k transferable powertrain warranty if you bought it new or had the warranty transferred.
Most of the trannies now dont even have a dipstick you can check so taking it to a dealer who has the scan equipment is your only option if this is a recurring issue .