Well mine does it too and I can pretty much duplicate it at will. It usually happens between 1st and 2nd like AtomHeart says. The other day I was coming out of a school zone just cruising in 1st, when a Caddy XLR is coming up on me. I speed up just a little and barely into 2nd gear, when he hits my bumper I shift down to 1st and punch it, and BAM!!! Instead of shifting into 2nd it falls flat and a half second later I'm flying after him. I was running about 30mph when I shifted down to 1st, so it's redlines pretty fast after I shift down. I didn't lose tracton at all and I had my TC off, as I usually drive with it off. I caught him pretty quick and he smiled and punched it and then I punched while in 3rd. He pulled on me about to his door when I caught up and pulled away. He didn't want anymore after that. I would have smoked him if the dang thing wouldn't of pulled the "ol' I'm sleeping mode".
It has to be when it's within a second of shifting because on the track it don't do it. Regardless if you light up the tires. You can roast them all you want and it never falls flat. This is with the TC off. So it has to be with the tranny shifting, and the TC. With the TC on it's a different story. Just a flaw we have to get used to.
Cruzinquick