My 1985 W150 keeps on stalling when I slow down to stop. The truck runs very rich and the idle screws have no affect on this. It is a 318 2 barrel. Ive checked for vacuum leaks but couldnt find any. The truck has very little power and the stalling keeps on getting worse to the point that it stalls at almost every stop light. Does this sound like a carb problem or a vacuum leak? Any help is greatly appreciated.