I have a 2001 Saab 9-5 2.3t. Two weeks ago I was driving for a fairly long amount of time, I had almost gotten back to my house and while I was going up a hill, the car started to overheat. I pulled over, shut it off, checked the coolant and it was full. I put on the heater and drove home and made sure to keep the heat of the car below the red. We assumed it was a broken thermostat so we took the car to the mechanic. The mechanic confirmed it was overheating and showed us how messed up the thermostat was so we replaced it. We started driving home and the car did not overheat and was running fine and all of the sudden it lost all of its power and the check engine light came on and started flashing. We took the car back and the mechanic and he hooked it up to the computer and it said it had a misfire in cylinder 4. He checked the head gasket for an issue but it was fine and then changed the spark plugs since we have not for a very long amount of time and he said they were very worn. We started to drive home and it happened again so we brought it back and he said the DI pack was cracked when he removed it so he thought that may have been broken as well. We ordered a new one and had it put in and we drove home and it seemed to run fine and it did not have another cylinder misfire but all of the sudden it stalled and would not turn back on. It got towed back to the mechanic and he said he thinks the DI pack that we got may have been faulty and he wants to replace it again. Is this actually possible or could my car possibly have some other issue? Any assistance would be greatly appreciated. Anything I can ask him next time I have to go see him would be great.