Either air intake is a nice addition...both are worth it.
Handheld tuners are NOT worth the $$$ in my opinion. I'd look into a custom tuned PCM by Wester's for example. Occasional GP's occur and these are much better tunes giving much more power than any handheld for roughly the same price. Do a search for Wester's ( or Westers) and you'll get more info.
A tb spacer gives minimal increases...some say it's worth it some say it's useless....mine did nothing but whistle.
Headers would be a good compliment to your truck. Thorley's, Gibsons, JBA, are all good choices.