Check your voltage at the receptacle or at your fused disconnect box. Check the voltage at your panel and at the point where the kiln is connected. Check the voltage when the kiln is firing and when it is not firing.
Ensure that no other large electrical appliances, such as a clothes dryer or electric oven, are operating when you are using your kiln.
Find out from your local utility company when the end of the peak period of electrical use is.
Check the wire size of your circuit. If it is very far (more than 50 feet) from your main circuit box then the wire size might need to be higher.