My 1997 GMC Suburban is stalling. At first it happened when at a stop sign or slow speeds, now it's stalling while driving higher speeds on the highway. It's done this about 5 times now over the last 3 weeks. The car goes dead, you lose power, and the battery and service engine indicators go on. I was usually able to get it to start back up again by shutting down everything (radio, lights, etc.) and then turning the ignition. Since last night, however, the car went dead for good and won't start beyond a little reving of the engine. I took the car in after the 1st time this happened and they told me some useless stuff about some carbon particle getting stuck in the exhaust and that "all the codes" checked out OK. Any ideas of what the problem might be?