The short is visible in the tire pressure light and the battery light. They flash when bumps in the road are hit? How are these related? And what type of shop could repair this? Is it an expensive fix or are they generally easy to find?
Problems like that can be extremely difficult and frustrating to find, especially if it can't be made to act up while sitting in the shop. It's impossible to drive a car safely and try to search for causes at the same time.
GM has a real lot of trouble with their generators since the '87 model year. A broken or corroded connection going to it can cause the battery warning light to turn on intermittently. When the generator stops working, system voltage will drop momentarily. Your car is full of many unnecessary, unreliable, complicated computers that are very sensitive to system voltage, so it's common for them to act up when the generator stops working. It's real common to read that someone's anti-lock brake warning light turns on at the same time, but any of a number of systems on the car can be affected.
The tire pressure monitoring system also uses a computer, and, both the generator and the computers get their power through one part of the ignition switch. An intermittent connection inside the switch or in any wire related to it can cause intermittent connections over bumps.
GM has done a real good job of preventing independent shops from working on their cars so you're sort of tied to the dealer for problems like this. If you have an independent shop in your area that specializes in auto electrical, they should also be able to find the problem. Plan on leaving the car with them for at least a few days. Unless they find something real quickly, they'll have to search behind the instrument cluster and under the hood, then perform a number of test drives to verify the problem is solved. Larger cities have many specialty shops that just work on electrical problems. There is so much work for them now because cars today have so many computers and are so extremely complicated. With the miles of wire and all of the connectors that develop loose or corroded connections, there can be hundreds of different symptoms and they'll never see the same problem twice. That means they're troubleshooting a new problem they've never experienced before. To add to the frustration, it can be almost impossible to provide you with an accurate estimate on the cost of repairs. The actual repair will often take just a few minutes, but finding WHAT needs to be repaired can take hours or days. If a computer is suspected as the cause, a new one must be ordered, programmed to the car by the dealer, then you hope that solves the problem. If it doesn't, the new computer can't be returned. GM has also figured out how to make salvage yard computers unusable in any other car so your mechanic must buy a new one.
The other frustrating part of intermittent problems is the mechanic very often can't know for sure if it's fixed. If the problem acts up again on a test drive, he knows it's not fixed. If it doesn't act up for him, that doesn't mean it's fixed. It might act up for you days later. THAT'S when he knows it's not fixed and he has to start all over. Problems like that create angry owners and give mechanics ulcers.