I'm looking into getting a TKO500 since my factory T-5 is about to take a dump, but am afraid it might actually slow my car down. I've heard tremecs weigh more than the T-5 and eat up more power. Will switching from a stock worn-out T-5 to a TKO500 hurt my performance at all?

Well, I did other things but I didn't notice any difference, except how much of a better tranny the TKO500 is over a T-5.