Slow as in slow cranking speed? That would make me think battery, or starter. A weak battery can cause all kinds of issues with modern computerized cars. The cooling fans are electric. I’m not an expert on this car, but if the coolant wasn’t properly filled then it could cause an air lock issue. Basically, air gets stuck in the water pump. automotive water pumps can’t self prime to get the air out. I’m not saying that’s your issue, but its a possibility. I’d start by having the battery and alternator load tested. Some auto parts stores can do this for free, it’s a simple test done on the car in the parking lot. Have you been taking it to a chevy garage? Sometimes there are things that only the dealer would know to do or check, it’s just a thought.