First off, a cup of DME probably weighs between 5 - 6 oz which added to four cups of water for a total volume of five cups would yield an SG of about 1.046, which is okay but a little on the high side for a starter. Also, I'm assuming you boiled it and had some of that boil off so it's probably a little on the strong side which could explain some of the delay.
It sounds like there is some activity going on. Rousing it frequently, as frequently as possible is good and will help blow off CO2 and give the yeast oxygen, provided of course that you're not using an airlock, which it sounds like you are. For a starter it's best just to loosely cover it with foil to allow air exchange.
I think it'll ferment out given some time. Just replace the airlock with some foil, wait, and rouse it up frequently.