1994 olds 88 shuts off while driving

my 1994 olds 88 royale will shut off without warning , usually after having traveled maybe 10 miles at 60+ mph. it will stop running as i brake for a stop or to slow turn. it has happened on the exit ramp, also when tuning on to the hi-way and when attempting a turn. this even happened in moderate traffic turning left with oncoming cars, which was an eye opener. the car will start right back up and drive ok. What could be the problem? it runs fine the rest of the time. thanks

If this is pretty much always at closed throttle (with your foot off the gas) then I’d probably start by cleaning the idle air control (IAC) valve.

If it is mostly associated with braking then I would worry about the brake booster and its vacuum supply line.