As a general rule you should probably be nice to it for a few hundred miles, perhaps a thousand. Contact the builder of the trans and ask them if you should change the fluid after the first month or so or if you should go longer.
i dont see whay you would need to change the fluid.. break in period on a transmission is normally 500 miles. basicly drive normal, no towing etc, and dont beat the shit out of it.
there should be no reason why you would need to change the transmission fluid, considering when u get a car brand new from factory, you still dont change the tranny fluid til about 30k
if its the E4OD, there strong trannys.. considering its the same thing ford used in the lightning.. some of them have issues, as did mine, but ever since mine was rebuilt its been great.. only that weird slipping problem, but i just got that diag'd, solenoid pack, which they dont usualy replace on a rebuild
Screw all these pansies. Run that baby hard and put it away wet and muddy. That's the only way to know if it is working right or not. If all you do is baby it you will never know what it can do.
so ive put 25 miles on it, and its slipped 3 times, and all my IDIOT lights have come on for it, both the Od light flashing and it going into limp mode then followed by the CEL.