What's symptoms of failing injectors PD Diesel?

[BIG F@ TW@]

Afternoon you gorgeous lot.

Just wondering what the symptoms are of failing injectors on a PD diesel engine?

I have an 05 130 B5.5 PD AWX and noticed that when starting sometimes I have to keep the key turned way longer than normal. Normally it starts on the button, but recently it will every now and then take a bit more on the cranking.

Is this the start of injector issue or is it more likely fuel pump issue? I have noticed that it doesn't like to be in low rev range in high gear either, so for example in 5th it will start to struggle at anything down near the 30mph zone etc...

Guy