There is a trick to taking them apart.
Use a rubber mallet to loosen the boards just a little.
Sawzaw with fire and rescue demo blade is your friend.
Start with the pallet standing up and then cut the nails holding the slats to the 2x4s on either side.
From there you can wiggle the boards some to lossen them more.
Use the sawzaw to cut those nails while holding the boards and saw at a slight angle.
Gravity with a Demon fire and rescue blade is all the force needed to cut any pallets nails. Even 16 penny nails are butter for it.
Once you get the hang of it, you can strip a pallet in under a minute.