318 stalling out in gear....

vacuum leak may be it, get a small spray bottle and spray around areas and shield it to that area with a piece of cardboard/paper. Does it die in all gears besides neutral and park? How new is the stall converter?

The reason I ask is I had a similar problem with my truck. I tried every damn thing in the book. Even after it blew a headgasket, it would still do it unless I pushed the brake and gave it a lil gas. My problem turned out to be someone put a 360 torque converter behind my 318. It wasn't very happy about that at all. After I got my transmission professionally rebuilt and a factory high stall, the problem went away.