I didn't know that you changed out the pump right when this started. Now I definitely think you have a blocked tank return line or you swapped the two lines.
It could be that you switched the lines at the pump side when you changed it out. That would have you feeding fuel into the tank return port on the regulator through the return line hooked up to the fuel pump outlet. That would push the regulator open to full pump pressure. The fuel filter is producing the back pressure on the fuel returning to the tank through the supply line. Maybe the filter has a check valve inside and the pump has a built-in bypass regulator at 70 psi?
What happens to the pressure when you put load on the engine? If it varies then you have no regulator action and that leads me to believe that you switched the lines. If it remains stable then I think you have a kinked or blocked return line and the pump has a bypass regulator inside set at 70 psi.