To much build up pressure in coolant system!

Looked at it a little more when it got home. Man did it stumble and misfire when I was backing up an incline to get into the driveway. Coolant was everywhere, so I rinsed most of it off with some water. And yes, my new overflow tank has a small hole at the top to relieve pressure. My dad revved it a couple times with it stumbling and popping, with white smoke coming out the tailpipe upon starting it up and deceleration. Trying to get the problem recreated but it wouldn't do it by just sitting there. Checked the temp of the fluid (no burps of air came out after 10 minutes) which was 185. Turned it off, checked the thermostat. It was open like it should have been. Checked the oil dipstick. May have been from the house down of the engine but there was some wetter bubbles on there. I'm fearing a broken head gasket/even a cracked head. My dad thinks we should look at the water pump next (that's also new, under a year old). Any other things to check to rule out broken head gasket?