94 surburban hard starting

i have a 1994 surburban that when you start it you have to floor the gas and then try and keep it running, black smoke comes out, but once you have it to idle it runs good but when you stop and try and go again it wants to
stall unless you just give it a little gas i have replaced the fuel pump and filter.now i changed the spark plugs, o2, map and throttle sensors and it is still the same.
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