If when you start your GE gas dryer the drum is not tumbling or is not tumbling at the right speed, you will need tom check the following parts.
The belt: The dryer use a very skinny belt that is about 1/4 of an inch wide to turn the tumbler or drum. With the age and usage of the dryer the belt tend to get stretched and this could cause it to slip and turn the drum at a slower speed. Sometimes when the belt is stretched is not able to turn the drum at all. So after many years of use, you should replace the belt.
The front drum bearing: The drum rides or slides on the front bearing assembly. This assembly consist of a plastic piece and four Teflon strips that the drum slides on top of it. With time and the amount of usage, the Teflon strip wear out and the drum starts running on top of the plastic support.
You could tell that the drum is running on the top of the plastic support because the dryer starts to make screeching noises and the drum won't turn at the proper speed. If you replace the Teflon strips on time, the you won't have to replace the plastic support. If you let it run on the plastic support, then you will need to replace the support and the 4 Teflon slides.
Rear drum bearing: The rear drum bearing consist of a shaft, a shaft support and a Teflon sleeve that the drum shaft rides on it. When the Teflon sleeve wears out, the shaft starts running metal to metal and the dryer sounds like a chirping bird. If the user continues to use the dryer like that, the metal will wear out and the complete rear bearing will need to be replaced. This situation could cause the dryer to tumble at a slower speed and it could even cause a not tumbling drum.
The motor: An overheating motor could stop in the middle of a cycle and cause the dryer to stop tumbling.