you did not mention spark plugs or coil?!? before you replaced all that stuff did you do a vacuum check? cylinder check? too often, shops ignore these 'old-time' tests & go for the electronics. the black smoke is unburned fuel. it may not necessarily be a rich-run problem, but could just be intermittent non-firing causing fuel to load up. you indicate that engine runs fine when 'stomped' on, does it really fire on all cyl's?