Sounds familiar to my focus turbo (petrol). When started first thing it'll stall straight away but starts up again no bother. It has water coming out the exhaust and I noticed it uses a little coolant. Had it 4 months and will just now need topping up. The car doesn't like heavy boost neither, especially 3rd, 4th and 5th but recently 2nd gear a bit. Breather system was totally clogged up with mustard colored gunk. Cleaned it out yesterday and seems to breathe better but still stutters. This all worth getting head gasket checked?