So I performed a drain and fill on my '06 Elantra (automatic) and was quite perplexed at the amount of metallic- looking sludge + flakes on the drain bolt. My tranny now seems to hesitate shifting into higher gears when accelerating (usually when trying to pick up speed on a freeway on-ramp?) Being low on gas also seems to exacerbate the problem. However, it is intermittent. Some days it works fine, other days it seems like my entire vehicle isnt running how it was the day before. Any ideas on why this is?