Can you help?
This is a 1994 GMC jimmy with a 4.3 vortec engine.
The problem is

1-- hard starting, -- turns over to many times before starting but it
Does always start. This is when it sets awhile, Starts ok if restarted Within a few min.

2---Rough idling but is better at higher speed.

3--At times when idling or at low speed it will sputter. This is most noticeable
After engine is hot.

4---black soot at exhaust pipe, This engine does not burn oil

Changed cap, rotor, plug wires and plugs, Notice that three of the plugs,
The ones from Driver side has what looks like black soot, not oil

At high speed this engine runs good with normal power and it does not Smoke.
Also, it has a new fuel pump and fuel filter.

I was told that gas is leaking into engine after turning off.
could this be because injestors dirty and would removing injectors and cleaning correct this problem?
Thanks,