For our 2002 Hyundia Sonata with 130K miles on its 2.4L DOHC 16 valve engine, the dealer says that they never replace the transmission filter during a transmission fluid change but only backflush the system using $6.00/per quart Hyundia 3 tranny fluid. They say that this is the only way to get all of the dirty fluid out of the converted which doesn't fully drain during a standard tranny transmission fluid draining. The fluid is a bit dark and has probably never been changed. The vehicle doesn't shift to a more economical gear until it warms up. I saw in some discussion on the internet that someone recommended ATF+3 and not to use an after market filter but the dealer says that they don't commonly sell this filter. This tranny would take the internal filter if it were replaced. What has your experience been in this area?