For starters, let's just start by saying this. Don't buy your scrolling blades at Lowes, Home Depot, or any other big box store. The blades they carry are sub standard and wouldn't cut butter if you heated the blade up.
Secondly, if it were me, and I was cutting 3/8" baltic birch I would probably use no less than a #3 reverse tooth blade. Preferrably a PGT blade (precision ground tooth) You might even go as high as a #7 reverse tooth blade. Olson, flying dutchman, king all make good quality blades. Personally, I use Olson.
To help you in selecting your blade, try this.
I'm not quite sure what you mean by the running in place. It almost sounds like you are not feeding the stock into the blade. The stock has to be constantly pushed into the blade and turned as necessary to follow the lines of your pattern. Make sure that you are applying tension to the blade. The DeWalt has a tension lever that slides from left to right. You want to tighten your blade so that when you pluck it like a guitar string, you will get a clear "ping" sound coming from it.
If you wish to check out my you tube page for a few tips and trick, you can feel free to do that as well. The address is in my signature at the bottom of my post. Let me know if any of this helps you and if not, we will carry on until we find the problem. I would hate for you to give up and deny yourself one of the most enjoyable and relaxing forms of woodworking that there is.