the under drives wont do anything to your tune but the power pipe will. it will allow the engine to get more air. the ecu should make up most of the difference with fuel but not all of it. the power pipe will allow the sc to make more boost which means you will probably want to run a bit richer. when mm&ff tested the power pipe they said they got ping after putting it on because of the extra boost
I would install the pullies right away, not worrying..as for the power pipe, I would install that and then get a dyno run and see if the air-fuel ratio has changed..it will probably be fine. 5.0L aren't as sensitive as the new 4.6L in the 99-05 models.