Overheating issues?

The thermostat failed so I replaced it and the water pump while I was at it. Now when I start the truck in the morning the temperature gauge will slowly start to creep up over the C mark but short of operating temperature. Then it will drop all the way to the bottom of the dial, the heater will start blowing cold air and within a quarter mile the temperature gauge will spike all the way to overheat. Open the hood and the reservoir looks like it's boiling and hissing out of the cap.
I have found if I'm driving down the road I can put the truck in neutral, turn off the engine and let it coast for about a hundred yards start it back up and the temperature gauge will return to operating temperature and the heater will start working again, which will do me for a few miles and then it happens again. Usually about the time I get where I'm going it stops giving me problems.
I have since flushed the coolant system, removed the thermostat, tested it and replaced it again, and then tried to burp the system all to no avail. I don't appear to have a blown head gasket so I'm trying to figure out another way to burp the cooling system or if an air pocket is even the issue.