how can i fix my renault master 2.5 diesel fuel problem?

I have a renault master 56 reg 2.5 diesel,it takes about 4 turns on the key to start then has no revs and drives at walking pace until the turbo cuts in at 2 thousand revs,but as soon as i go to change gear and the revs drop i am back at square 1. It will do this all day and as i am a multi drop delivery driver it is hard work,i have had new glow plugs fitted and a diagnostic says there is no faults,any idea's? Please help