99mustangbeast

hello i have a 99 ford mustang gt 4.6 sohc this is the problem i do not have a over drive. I push the od button and doesn't light up on the dash. On a slow take off right about 30 mph it slips and goes back to normal. On a fast take off i don't feel anything. The transmission went out. I replaced the transmission used one. An i have the same problem two transmission same problem whats the odds please help