Dies Occasionally

2.7 engine. This vehicle has recently started dying occasionally at stoplights. However, it always starts back up immediately. Some days it runs just fine. Other days it may quit 4 or 5 times. No codes. The spark plugs were changed at 100,000 miles. It was dying before the plugs were changed and then the problem ceased until just lately. I have put injector cleaner in the gas tank the past 3 times when filling up. Without a code, I don't know what else to do.

Also, how far should the temperature gauge rise? Recently, a local mechanic changed the thermostat. However, now the temp gauge only rises to the first mark and stays there. Never goes any higher and then drop back down when the thermostat opens. Is this normal? I thought there might be air in the system or the thermostat was faulty. He put another thermostat in it last week and with the same result. It's a 185 degree thermostat but a computer says the coolant is 180 degrees when fully warmed up.

I'm not sure if a false temp. Reading could cause the dying problem.