Dies and won't start back up

We recently bought a 97 GMC Sierra after having it
for about a week it died on us while driving after it
set a few hours it started right up and ran for about
another week then we pulled up to get gas stopped
to back up and it died, this time it wouldn't start
again (it would turn over but not start) so we took it
to a shop where they charged us $327 to tell is that
they couldn't figure it out that it was probably the
computer that they couldn't fix it....we then took it
to my uncle several hours away he replaced the
ignition control module and it started so we picked
it up drove it about a week....then today it was
running but in park and suddenly died and wouldn't
start again please help we bought this truck for my
husband to work out of and it's the only vehicle we
have with air!!!!