toyotaguy, you don't know me and I certainly don't expect you to take my word for it, but do some research and you'll see that regardless of what the manufacturers and their minions would have you believe, there's no such thing as a lifetime fluid, or for that matter, a 100,000-mile fluid. You are absolutely right to change it out early. HOW early is a matter for debate, but 50,000 miles is not too early by any means, especially for a simple drain-and-fill.
I do agree that you should use the Toyota WS unless you can find an aftermarket fluid that clearly states that it's approved by Toyota. Note that I said "approved by", not "recommended for" or "suitable for".