Your best bet would be to read this article here:
It's a guy who rebuilt the 5R55E predecessor the A4LD into a 5R55E. Not sure which variant of the 5R55 you have, but they are a good news/bad news situation.
For the most part, the latest designs have mitigated the vulerabilities of the original design. Your transmission is a descendent of the venerable C3 that was the automatic in the Pinto, lol. It's been with us a long time.
I'm in the process of rebuilding mine and though it has only seen service behind a 3.0, I've beaten on it HARD offroading my 2WD with 35" tires and keeping up with 4x4's.
I'm only rebuilding it to put the 4x4 output shaft in it so I can finish my SAS and make my truck a 4x4. Otherwise it's fine.
I recommend Royal Purple, Redline, or Amsoil (my personal choice) fully synthetic transmission fluid. It reduced my tranny temps and smoothed out a lot of shifting glitches when I did a flush-and-fill with it around 30K. I have about 90K on it now.