OVEN UNABLE TO HEAT ABOVE 350 DEGREES

If it was an electric oven, it would likely be the heating element itself. But since it is gas, we have to look elsewhere.

The most likely culprit would be the temperature sensor inside the oven, & that is not registering the temperature correctly. It is saying that it is a different temperature than the oven really is, so that you cannot get it to go higher. Typically this would not be a user replacable part. If you can find your manual for the range, you would be able to tell for sure if it is user replaceable or not. If you need to call for service, GE has a reasonable price for their service calls - and they can also check the range and oven nozzles etc to make sure they are functioning correctly. Or put another way, you can have them do a preventative maintenance check on the whole thing while they are there. Be sure to tell them what you know it is doing ahead of time as well as the model and serial numbers, so they can have at least some of the parts with them.

Good luck.