Autotune PID VI - getting an accurate reading

Hello,
I am controlling a voltage controlled relief valve (which in turns controls the load applied by a press) with a LabVIEW code using the Autotune PID VI. Our setpoint is a load as our process variable is a load measured from a pressure transducer. We are able to use the Autoune VI to tune for low loads, however, the process is quite slow to get to the desired setpoint. Then when the speed is increased (the proportional gain increases here) the VI is unable to tune properly. Furthermore, when the SP load is changed rapidly, the VI is unable to tune.
Can anyone help with providing a method to get the Autotuning VI working consistently with a reasonable speed? I have attached an image of the code I am using to give you a better idea of what I'm trying to do.
Thanks for you help.

Hi Jazz,
The slowness of the VI is caused by the VI repeating over and over. Unfortunately there is not too much that you can do about the speed. When you increase the proportional gain what is the problem that you are getting? If it just tunes to a different value that could be caused by a different min/max. If you could give me a little more information that would be helpful.

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temp.JPG ‏38 KB

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