I have a 2006 trailblazer with 194K has ran good for ever but I was getting a #6 miss fire for some time. But never any engine problems. Till about a month ago started to idle rough and stutter at take off. So I replaced the #6 coil pack and that fixed that code but now I am getting P0300 Multiple Misfires and P0128 coolant temp below thermostat regulation temp. I have read 100 or so of these post and nobody actually says what fixed problem. Catalytic Converter, all new coil packs, thermostat, ECT sensor. Anybody solved this problem if so how. I replaced the CPA and that helped it was clogged. Last oil change I had them put in the High mileage and I think it broke up some sludge from the bottom of the pan or something. Change the oil ran fuel cleaner through it?