New variable speed pump loosing prime at low speed

[lucas2]

OK, the problem I am having now, is that I cannot get the vaccum pool cleaner to work. I have been messing with it for 2 days and it is almost like there is a partial restriction in the suction line, and the vaccum puts it over the edge with the extra friction. Is this possible? I am thinking of back flushing it today with a hose and seeing what happens. Wondering if the suction leak was helping pump before?

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Also, I have replaced all above ground piping, super sealed all joints, removed unions, brand new pump, new o ring in 3 way valve. There is nothing left to check except underground pipes. How do I go about this, and what should I be looking for?