P0190 Fuel rail pressure (FRP) sensor - circuit malfunction Wiring, FRP sensor, ECM  
Put a mechanic guage on it and check the pressure...

Have done that, fuel pressure is fine at idle and drops under load to as low as 10psi.. Ford also saw the same, although they told me that the fuel rail pressure sensor was requesting more fuel pressure than what was seen at the rail so that is what lead them to believe the issue was the pump.
 
There is a fuel pump driver module under the drivers side back seat, so I am now trying to figure out if that could be the cause.

How many wires does the fuel pump controller have? They are easy to test generally as you can bypass them.

Hi Phil, there are six wires. I should be able to figure out which wires go to the pump. 
 
These may sound like silly questions but how do you securely connect the multimeter? I assume it is voltage drop that I would be looking for?
 
Thanks.

Sounds like the same set up as Turbo and 6 Cyl Subaru's run... The wires to the unit will be 12v from fuel pump relay or fuse,GND, +ve out to fuel pump, -ve out to fuel pump, 2 wires from ecu, one will be a reference voltage and one will be a switching to gnd to produce a variable duty output....exactly like an injector would use. The ecu sends the injector pulse type duty signal to the fuel pump controller, this varies the voltage output to the pump. I have just finished diagnosing and repairing a car that had the same issue. I found that when operating normally at idle etc there would be around 8v going to the pump, when under load/accelerating the voltage should go up to 12vish. You can also check the signal from the ecu easily with an oscilloscope, actually if you have a 4ch scope, you can monitor the input voltage and output voltage as well...very easy to see where the issue would be in that case.

The fuel pump controller is a bit like an electronic speed controller for a RC car.

Hi Phil,
 
Thanks for that. I might see what I can do with the multimeter. The problem is somewhat different to before and has become more of an intermittent problem. The car seems to be fine when its cold (maybe a little jerky), although when it gets hot (this could be after 20mins of driving) the problem arises and it is more of a violent missfire what gradually worsens until the car eventually stalls. Turn the key and the car immediately roars to life and I am away again for about 5mins until the issue reoccurs.

If you diagnose the problem and is a ST part only(not std Focus) and you need parts, Athol Park Ford wreckers(Adelaide) have 2x ST170s, including my smashed 1, which was going great at time of the stack! 
 Good luck 

Alternator voltage control fault perhaps, or heat soak in the Alt?
Check the voltages when hot

Hi Marty,
 
I called them and unfortunately the fuel rail pressure sensors are gone. I thought I was in luck.
 
Stevie, that is worth checking and I have looked into it somewhat.