What could be making my Bonneville not run?

My Bonneville starts but runs very rich for a few minutes, then seems to get
itself worked out of it, runs good for about 2 minutes and then completely
quits. The only code the computer is saying is for a vacuum leak but I just had
all the intake gaskets replaced and hoses checked. And it does the same cycle
every time you try to start it - runs rich - to being okay - to quitting. So far
we've replaced the battery, intake gaskets, crank sensor, MAF sensor and map
sensor. The fuel pump and alternator were both tested as well. Anyone have
any suggestions as to something we might be overlooking? This has all of us
stumped...