If you double the speed of a pump you will need eight times the amperage. The increased amperage can be caused by a change in the product. The motor was sized for a low specific gravity fluid, but the lines are being flushed or tested with water. The specific gravity of the fluid you are pumping has increased for some reason. The viscosity of the liquid is increasing with a change in temperature.
Some viscosities increase with a lower temperature, some with a higher temperature.
The viscosity of a liquid can increase with agitation. That is how cream becomes butter. Two parts rubbing together when the shaft displaces can cause the increased amperage. This can also happen with an improper impeller adjustment or thermal growth. The end of the stuffing box can be rubbed by the shaft or sleeve.