[SSmokinem]

Don't flush it...

Drop the pan, do an internal if you want, and the external filter, replace the pan and fill to proper level at operating temp, drive 500miles, drain and fill and do another external filter.

Flushing the trans isn't always the best idea, especially when you don't know how the rig was previously maintained.

I've seen guys that flushed a trans when buying a higher milage rig cuz they thought it was the right thing to do, only to have it done wrong or have debris get lodged in the valve body and make pressure switches and valves stick in the valve body, then the trans failed