That's right - I just did a drain and fill on a friend's Hyundai XG350L with the five-speed auto. It specs Hyundai's SP-III fluid, but that stuff costs $gold around here so I bought some Valvoline Maxlife Dex/Merc and put that in instead.

It shifts like absolute butter now! It's unbeleivably smooth. I didn't think a simple drain/fill could have such an impact!

Some notes:
-These transmissions are super easy to work on. Has a drain plug on the bottom (imagine that!)
-The fluid that came out was dark brown and very little smell to it.
-Drain/fill replaces about 5.5 qts. Total capacity is 9 qts.

The car has 85k on it. Fluid might have been changed around 30K by the dealer. Assuming the previous fill of SPIII was run between 55k and 85k do you think I should wait a day or two and do another drain/fill or could it be left for 15k or so?