Engine goes rich and wants to die.

I bought my dart a couple of years ago, it came with a reasonably built 340, a 3000 plus stall converter, and 4.56 gears in the back. When I first got the car you couldn't drive it very far because the thermostat was too high and would get up to about 215 deg and would get too rich and die. Well I fixed that right away and put a 180 deg. thermostat in it. Since then I have rebuilt the carb and put a new intake manifold on it not all because of the going rich problem. Now I can drive it at lower rpms all day, but if I step on it and shift it through the gears when I come to a stop the car still goes really rich and wants to die.
Any ideas of what it might be? Thanks for your input.

Patrick