Oven achieves but does not maintain temp

GE Spectra Electric Range
Model: JB960C084CC

Problem:
Oven achieves the set temperature.
The oven cools without maintaining the set temperature
BUT the digital display keeps showing the preset temperature.

Example:
•Set oven to 375 degrees.
•Display begins at 100 and increments until 375 is achieved.
•Wait 15 minutes
•Turn OFF oven.
•Reset oven to 375 degrees.
•Display begins at 352 and increments until 375 is achieved.

Thanksgiving Day is a BAD time for this to happen.
We had to keep resetting the oven every 15 minutes to keep the temp up.

Any suggestions?