The vehicle is a 1997 Ford F250 apx 150K miles.

The engine seems to be running fine. The problem is when I am at a stop after
About 30 seconds the engine starts to "chug" like there is air coming from the exhaust.
The truck has died a few times but always starts right back up with no problems.
The battery gage is above half. What could this be?
Thank you for your assistance!

I would change fuel filter at the least.
If tune up has not been done for a while, would do plugs, points, cap, rotor, wires? air, oil, and oil filter at the least, That may solve the problem and should eleminate those as a possibility.