My Mother-in-Law has a 2003 Chevy Avalanche with the 5.3 with over 200,000 miles which has been very well maintained but today she started having problems which seem to be electrical. She just put a new battery in so I think that is a eliminated problem however, when your driving its fine, but when you let off the gas pedal the vehicle wants to start shutting down and gauges start acting weird. I thought problems with the alternator but seems more like a vacuum problem or possibly the main computer. Any thoughts?