Re: auto trans problem
If you've been driving the truck with the O/D Off light flashing, then that's not too good for the trans. No other trans will fit in your truck except another similar trans from a Ranger or Mazda B-Series truck with a 3.0, and maybe the 2.3/2.5.
As for the fluid, have you been checking the fluid while the truck is hot, and has gone through the gears? Checking the fluid cold doesn't really get you an accurate reading, and within the time it took you to remove the excess fluid, the trans could have cooled enough to make the fluid cool, resulting in your lower reading.