Skip the full sump of ATF.. in fact skip the ATF in your oil completely. If you must do something, then do as others have suggested - Run an OCI or two using Rotella 10w30.
Better yet, depending on the oil that the engine specs, use the Rotella 10w30, but replace 1/5 to 1/4 of the oil with MMO. You mentioned red/pink coolant, so I'm going to assume that this is an asian car, and thus would most likely spec an oil lighter than 10w30.. and so the MMO will lighten up the oil, and might help a little in clean-up.
.. In all honesty, though, the Rotella will do some good cleaning by itself. Way better than any ATF could.