Just to be clear, you did change the pump? If not that is what needs to happen.
By raising the RPM you are increasing the pump pressure so we either have a pump issue or a restricted line.
I would flush the system and if it still does it then I would put a new pump and belt on it and retest.
Below is the info on this. Please let us know if you have questions on this. Thanks
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Monday, June 7th, 2021 AT 3:18 PM