My Mercury Stalls only in gear!?!?

I have a 1993 Mercury Sable that runs low rpm while in gear and always dies when I come to a stop. I've changed the fuel filter and their seems to be no vacuum leaks occurring. The car drives fine on the highway or at a constant acceleration. I have to 2-foot the car which still doesn't work half the time. Also the car seems sluggish when I give it gas but only from 750 rpm to 1000 rpm does it do this. Any help at all would be very Appreciated.

Thanks