I strongly recommend that you install WeBWorK 2.19 instead. Archive any courses you have, and follow the 2.19 installation manual to install. Then unarchive and upgrade the courses.
Note that PGUtil.pm is a PG module, and you won't find it on CPAN, and check_modules.pl doesn't check for PG modules. If webwork2 isn't finding it, then you don't have something configured right with the webwork2 setup. I believe for WeBWorK 2.16 you needed to have the PG_ROOT environment variable set to /opt/webwork/pg for that.
You mentioned checking out running "git checkout tags/WeBWorK-2.16 -b upgrade-to-2.16". In the PG directory you would need "git checkout PG-2.16 -b upgrade-to-2.16". (You don't need the tags/ prefix on the tag name.)
Note that PGUtil.pm is a PG module, and you won't find it on CPAN, and check_modules.pl doesn't check for PG modules. If webwork2 isn't finding it, then you don't have something configured right with the webwork2 setup. I believe for WeBWorK 2.16 you needed to have the PG_ROOT environment variable set to /opt/webwork/pg for that.
You mentioned checking out running "git checkout tags/WeBWorK-2.16 -b upgrade-to-2.16". In the PG directory you would need "git checkout PG-2.16 -b upgrade-to-2.16". (You don't need the tags/ prefix on the tag name.)