My GMC Diesel Truck began stalling shortly aftern starting in the morning. The frequency of stalling was reduced after I changed fuel filter. However it resumed. I took it to Diesel Doctor an they tested fuel system and thought the problem was a failing PMD (Pump mounted Driver). The would replace it for $905. I chose not to do that since I new I could order a PMD onlne for about $300. I purchased one on Ebay for $220. Since the Diesel Doctor Diagnosis the truck has not stalled one single time and I have not yet installed the new PMD. So I think they misdiagnosed the problem and accidentally fixed the unknown problem while testing the fuel system. I assume somehow air was getting into the line leading to the engine stalling. Also the quote on replacing the PMD was way out of line of the actual cost of replacing it, a 15 minute job at most. I can give Diesel Doctor credit for having the truck for one day and not keeping it overnight. Cost of diagnosis was $259 and I think maybe this was a bit high. But they did go ahead and do general look over of the vehicle, which I had not asked them to do, but also not asked them to do. They identified some problems I was not aware of.