You can inflate the flat tube to see exactly where it is punctured... then check your tire at that spot to make sure you are no missing or failing to catch a thorn or piece of glass. Also check the tube... is a puncture or is the seam splitting? I once bought some Performance tubes that were all defective and split along the seam. Also what size are your tires? Its hard to tell if you are overinflating or underinflating... both can cause pitch flats.

Is there some reason you like those slime tubes? I just use good regular tubes and never flat. If using slime tubes... don't you just spin the wheel and re-inflate the tube? Have you tried that? The tube should stay filled with air if you give the slime time to set. The whole purpose of those nasty messy tubes is to be able to use them over and over again...