It doesn't take much juice to keep the engine running - if it had plenty of crank, it had plenty to fire the plugs. So I don't think that's it.
The "hiss" is an attention-getter, but I think it's a red herring: Do you mean while it was still running fine, and the wipers were on, you heard the hiss? If the hiss is heard with the wipers off, then it's a vacuum-leak. BUT, the line to the wipers is small, and I'm not certain it would kill the engine like that. Definitely cause a rough, poor idle, and maybe since you were on a down-ramp with your foot off the gas, it died at idle. Anyway, it should be checked - be sure the vacuum line didn't fall off or suffer a melt-down. If you think it's a potential problem, for the immediate situation, plug the line - maybe crimp the hose close to the source, just to be sure it's out of the equation.
Checking fuel is a good first stop. A plugged fuel filter I wouldn't think would kill it cold turkey - usually, it leans out the fuel, and the engine sputters, or it will die, but start up again. But, definitely worth checking for fuel at the carb.
Stock engine? Original 216, I think? Or upgraded 235?
Take the air filter off and look down the throat of the carb while you operate the throttle briskly. See if there's a squirt of fuel in the throat of the carb. If not, it could be the fuel bowl is empty, ie: not getting fuel. Are you certain your gas gauge works, and you're not out of gas?
While you're there, double-check that the choke and mechanism is operating correctly, and that it hasn't flipped closed.
Once you're confident it's getting fuel, it's time to start checking spark.
Others smarter than me will chime in - post back with your findings.
-Michael
