renault master van will not start cold or hot?

my renault master van will not start without the aid of easy start, this is needed cold and hot starting.
Occasionally it will stall under load and at low revs, ie just before you need to change down when going up hill.
turn the key off and immediatly back on and it restarts.
I have replaced the glow plugs and injectors.
the renault garage is useless and has no ideas, what else can i do.

Sean
January 2009