95 Buick Regal randomly turns off

I have a 1995 Buick Regal that will randomly shut off while
driving at speeds lower than 35 miles an hour, if I take out
the key and restart it, it turns right back on. It is worst in the
heat, and had no trouble during winter.
Since summer hit I have barely been able to drive it for
more than two stops without it begining to turn off. If I have
to shut the car off, then turn it back on, more than twice in a
day it is pretty much done for the day and wont start again.
Putting the car in park seems to aid in the issue also.
And when I am on a slop my gears are hard to change from
park.

If I really have to run errands that can't wait I will leave the
car running while I run into the store or bank, ect., to
prevent it from shutting off., which helps a little but not
much, since even putting the car in park, seems to also aid
in the issue, it also makes the car heat up from It running in
idle for so long , so it starts to run pretty rough because of
that. So running errands are out of the question now pretty
much.

I have had so many things replaced and looked at, but no
luck.
Any body have any idea what the problem could be?
We dont have money for a new car, and im sick of putting
money into this one with no luck.