End Of Rope /please Help

[slugish]

HAVE ANY OF YOU HAD VAPOR LOCK PROBLEMS & IF YOU HAVE , WHAT ARE THE SYMPTOMS & WHAT DID YOU DO ABOUT IT. SOME TIMES MY 400 WONT CRANK AFTER ITS HOT & EVEN HAS A HARD TIME CRANKING AFTER ITS COOLED OFF FOR A WHILE, BUT IT WILL EVENTUALLY CRANK & RUN FINE TILL NEXT TIME & WHEN I GET IT BACK CRANKED IT WILL SOMETIMES BACKFIRE AT CRUISING SPEED.
FOWLED PLUGS ( DO GET GAS & OIL ON THEM ) CHANGE OFTEN BUT LAST TIME WERE NEW PLUGS IN WHEN IT WOULDNT CRANK .

HAVE ALSO REPLACED MSD BOX, COIL &DIST CAP & ROTOR.

LAST GARAGE I HAD IT TOWED TO , THEY COULDNT GET IT TO ACT UP
BASICALLY COULDNT FIGURE OUT WHAT WAS GOING ON .
ANY SUGGESTIONS OUT THERE?