I have heard conflicting opinion. Does a HFC change/improve performance on an otherwise stock exhaust? Does it need a tune change? What is the consensus on this issue? Thanks!

yes it helps.

I just got mine on a week or 2 ago, it helps, but like almost anything else, to take full advantage of it you'll need a re-flash.

the only bottleneck on the stock svt exhaust is the cat. Get a tune from tom as well, asap! Really helps at this altitude as well.

I have Toms tune do I need a reflash?

Since you have a tune from Tom all you need to do is contact him, tell him what you've done and have him send you another tune.... since you get free tunes as you upgrade you may as well take advantage of it.

How hard is the instal? CFM vs Jay racing ?

5 bolts, 2 O2 sensors... thats pretty much it.

my svt came with a orp on it but also came with a long list of abused parts

^^^who was the owner?