Toyota Hilux: Hard start when cold

Have a 2010/2011 Toyota Hilux. Engine is a 2.5L diesel (2KD-FTV).In the mornings the engine is hard to start. 

Changed primer pump & diesel filter. Still same problem.

Dropped fuel tank & cleaned fuel strainer (was blocked & covered in algae). Still same problem.

Removed glow plugs & checked resistance, all within spec (0.8 ohms).

Took a graph of fuel pressure vs. engine rpm. Not too sure if what I see is correct? The fuel pressure increases & gets the engine almost starting & then it drops rapidly.
Shouldn't the fuel pressure be relatively constant?

We also notice that you you have to press the accelerator to get the engine starting faster.

Leaning towards the high pressure fuel pump but looking for some input to justify ordering the part.

Bumping thread to see if any takers on the captured graph.

Also bumping because I had a Toyota Hiace van with the exact same engine (2KD-FTV) come in with a similar problem.
Engine cranks & then takes too long to start. I did however notice that if you crank the first time & leave it cranking the engine doesn't start. You have to crank it for like a second or two & then cycle the key off. Cranking it a second time then gets the engine starting straight away (this method works all the time). New diesel filter & primer pump has good suction. Scanned & no fault codes. I'll update with additional checks as called it a day.