My only suggestion is to see if you can bypass the pressure switch (that determines cut in/out pressures). With the pump continuously running - determine the maximum pressure of the pump with a gauge and verify that pressure/ flow is adequate upstairs.

Perhaps you can change or adjust your switches (depends on model), so that the cut off is ~5-10psi below this maximum.

If pressure/ flow is not adequate with pump continuously running - new pump will be required.