Volvo engine? These aren't a Volvo engine as far as I'm aware, the later 'DW' engine that are Ford/PAS (French *spits*) were used in Volvos also. Your engine is the 'Puma' engine, were used in Mondeo,Transit,X type, Fiat Ducato,LDV vans amongst others.

Leak off test needs doing and fuel pressure tests as I've posted above. More than likely your fuel pressure is dropping on high load situations then PCM is shutting off fuelling.