I don't know which of your products to use on my deck. In 2002 and 2003, I
applied TWP 316 (light cedar) to the deck. It was beautiful when it went on, but
not so hot now. The finish completely failed in the parts exposed to sunlight,
but is intact in the areas that are shaded. Which product do I use to remove the
finish: Powersolve, Defy, or HD 80? Also I have fir posts and Powder coated
green iron railings, so I don't want the stripper to affect the finish on the
railing. The railing is 4in above the deck.

After the stripping is completed I was planning on applying a coat of Wood Tux
to the IPE. Good Plan?

I would use either the Powersolve or the HD80. The Powersolve is easier to apply. Makes sure you brighten to neutralize the stripper. The stripper should not effect the railings but test a spot first and constantly rinse. Same with the brightener.

Wood Tux works very well on hardwoods. The problem is your type of wood requires a maintenance coat on an annual basis.