Fuel pump problem is very likely. Had a couple do very similar things.Check the fuel pressure, should be 40 with Sbec III.Very rare but it is also possible that the fuel press reg might be bad.(it's on the rail)BTW 3.9L and 5.2L in 92 were both SMPI w/return fuel.All Magnums 1993 3.9L,5.2L,5.9L and up were returnless fuel system.Fuel press regulated in the tank by the pump.