Kickdown stalls until 5k rpm

Hello everybody and thanks for the add to the forum if I'm not doing this right I'm sorry I have never been a forum person... So this is what I have I have a 2000 model mustang gt with the 4.6 and stock aod tranny only mods I know of are flow master exhaust and cold air intake... What happens is when I'm driving the car drives and shifts perfect while I'm running about 50mph and wide open throttle it the rpm runs up to 5000 and then it kicks down so hard it barks the tires I have had fluid and filter changed and still no improvement I'm desperate thanks in advance