1993 300se stalling

[coach3062]

I have a 1993 300se 6cyl, over the past MONTHS it has stopped whilst driving. Initially it would go 20klms then gradually shorter distances.
When it stops it is like running out of fuel (firstly a stumble when accelerating, then gradually going from 6 to 5 then 4 cylinders and stalling). Fuel filters have been replaced twice and were clean (I cut them open), fuel pumps were replaced, fuel pressure regulator was replaced, the local auto club mechanic tested the ignition side and said its ok. The car will start again after about an hour or so, then repeat the stopping.
As I have other cars I haven't chased the problem hard but now my wife is on my back saying nasty things about my german girlfriend.
Does this sound like a fuel pump relay problem, or what do the informed members of this forum suggest?