I honestly think Nissan should have transmission services done earlier than 20,000 miles. I drained out my transmission oil at 12,000 miles and there were very fine metal shavings that added a glistening effect to the gear oil. I put in some Amsoil 80w90 GL4 and it's been shifting like butter for the past 3,000 miles. I'd suggest swapping the transmission fluid as soon as possible for people with 03-04's before they get this problem.