jackrae:
It looks like you have too much thermal mass for your size of heater since there is substantial lag even with the heater fully on.. And you need a method of cooling that mass when ramping down - say a fan blowing ambient air.
guilty as charged!
fan for the cooling stage is next on the list
insulating the oven may help too
oven is 1kW, 9 litres
but I have blanked off the lower 2/3 so effective heated volume is around 3 litres
I also moved all the heating elements to the top as well