bmw 330d se 03 reg?

Hi I have bmw 330D SE 03 reg it has developed a probleme,when over taking on 4 gear at 4000 rev the glowplag worning light come on and there is loss of power but when the rev is keped between1600 and 2000 rev there is no probleme but the driving is verry slow specialy in the motorway can you please explane how can it be fixed and how mutch it will cost and thank you.