Like Juanitad, my tongue also feels like it's swollen when the speech problem comes up. It's like the back of my tongue is just too big for my mouth, and the tip of my tongue won't go where I tell it. I tend to think of my mouth as going flat-lipped. It won't form any shape but the one it's in when I'm not speaking. It comes out nearly unintelligible - try speaking without pursing or shaping your lips at all (open or closed are your only options) or your tongue, and you'll see what I mean.