All lights interior and exterior Flicker slightly

Flickering lights is not uncommon on any car model, but GM products have an unusual problem that you should be aware of. GM has had a very poor generator design starting with the 1987 model year. You can expect to go through four to six generators in the life of the car. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. Due to their design, these generators produce huge voltage spikes that can destroy the internal diodes and voltage regulator, and interfere with the many computers on the car. As the battery ages and some of the lead flakes off the plates, it loses its ability to dampen and absorb those spikes, even though it cranks the engine just fine.

You may be having an issue right now with the voltage regulator trying to respond to those voltage spikes. What I would suggest first is to look at how old the battery is. There is a fairly good chance you still have the original battery. If so, at nine years old it is way past its life expectancy, so buy a new one. Have it installed where you buy it. They will use some type of "memory saver" device to insure no computers need to be reprogrammed after the battery was disconnected. If the flickering continues, have the charging system tested by your mechanic. In particular, I want to know what is found for "full-load output current". A typical value is around 90 amps. If all your generator can develop is exactly one third of its maximum rating, it has one defective internal diode of the six. That can be blamed on the old battery. If only the generator is replaced and the old battery is not, the same failure will occur again in short order.

If your battery appears to be less than about two years old, the generator may have developed the same problem some time ago, so testing the charging system is still in order. As part of the test, your mechanic will still test the battery, and if it is okay, leave it alone.