When is it time for a tune up?

I bougt this 5.0 a few months ago and supposedly the engine was "rebuilt" about 15k miles ago. Well, it has TFS TW heads, #2 cam, GT40 intake. When I dynoed it the first day I owned it, it only dynoed at 247RWHP/287RWTQ. I was not worried about it because it still had stock headers, crappy o/r h pipe that had some kinks in it where it may not have even been 2.25", and a crappy catback. Now I have replaced all of that and it does not feel great on the power end. I have not had it re dynoed yet, but I am wondering if a tune up will help. I know the timing was only at 5* when I checked it recently. That is because the distributor will not stay tightened down.

So can a tune up help me? Is this a good deal?

Tune up kit

Also, how can I keep the distributor tight if the bolt that holds in in place is not staying tightened down? When do I know if I need a whole new distributor?

I figured since then engine was rebuilt fairly recently, it would have had a tune up done. Thanks.

Yeah, I do not know why it will not stay tight. It tightens down, but then a few days later it is rotating again.