I did another drain and fill last night, fluid was still a little dark, converter must hold more than I thought, but that's 24 qts total ran through it. I'll def service it at 25k next time.
takes about 24-26 quarts to flush the system with new stuff. i usually do the "hoot method" or just pull a cooler line and drain 5 quarts into a bucket, refill, repeat till fresh fluid comes out.