I think I'm an very good ddr player. I have really good sight reading chops but I have a problem. It seems that when I play a song twice in a row I do much worse the second time around. I think I can't shut my mind up and "overthink" the game the second or I can't think at all. Any thoughts?

Yes. Make sure you're not learning it wrong. If you get 20 greats followed by 35 greats then you're either tired or you're timing it completely wrong. If you're whoring a song out then use left/right/mirror/shuffle to force yourself to pay attention.

That's a great idea Catastrophe. I think the main problem is not learning it wrong. It's just when I play a song again after playing it I just freak out, overthink and over-react. That idea using mods is great however. I would of never thoght of that. Thanks.

I'd suggest not playing the same song more than once in a row.  Go through the song wheel, play songs that you haven't tried before, play songs that maybe you wouldn't normally play.  Keep your mind flexible and improve your overall skills rather than tightening up only on selected songs.

Also, when you learn songs well enough, the "overthink" problem tends to solve itself, I've found. I get past the question of when to step because I know the rhythm by heart, don't have to think about it, so I only have to think about *where* to step. That makes it a lot easier.  And if I'm having trouble figuring a song's rhythm out, I go into training mode, turn the song+handclap assist on, and run through it a few times.  That drills the step rhythm into my head pretty quickly.

Maybe you are thinking, "Oh, I totally passed this song before.  I can just mail in this stage."

I agree that you can overthink.  Instead of thinking, listening would be better. ;) 

I have trouble with some of the more technical songs. I usually don't think about what I'm doing when I dance, I just do it; but with some of those technical songs where theres like, a difficult set way to step the arrows, and they're all condensed, I usually screw it up.

And a lot of the songs that do this I can't play on training mode, because they're on the arcade machine.

Using speed mods lets you ignore what you think is comming up and forces you to be more intune with the beat.