Intermittent problem

[teammadden]

I have a 2001 sea ray 5.7L EFI TBI mercruiser with about 350 hours. After running for awhile the engine will start to miss/choke out while running. I get a lot of soot on the transom and the tach will jump even though the engine is not surging. I can turn it off for a few minutes and run again sometimes for several hours before the problem comes back. I cannot reproduce the issue at home out of the water. I have also ran several days without the problem before it come back. Here is a list of what has been done. Any ideas would be appreciated......
New Plugs
New Plug wires
New Dist. Coil
New Dist. Cap, Rotor and sensor wheel
Drained Gas tank cleaned pickup
Gas tank vent clear
New gas
Replace anti-siphon valve
New water seperator filter
Fuel pressure checked ok
Checked resistance on air temp sensor ok
Checked resistance on engine temp sensor ok