The trans takes Mercon/DexronIII only and it stop being labeled that in June of 2007. Napa sells their own brand made by Valvoline that meets the same standards as Mercon/DexronIII it is simply called ATF, you will need about 20quarts to do a full flush, but capacity is 17 quarts IIRC. Don't let anyone tell you Mercon V is okay to use, even though Ford wants you to believe it.
Your rear axle in the dually is a Dana 80 and takes synthetic 75w90, IIRC 4 quarts will do it
The front axle takes the same fluid. You should have a LS in the Dana 80 and therefore you need to add the anti friction additive, don't add 80z that Ford says, this is why their LS has a bad reputation. Add 3oz and do some tight figure 8's, if you have chatter, add 1 0z at a time until the chatter goes away and your LS will work as designed.