The gamalg package doesn't seem to be in 5.9.3.
This code, written by Stephen Wolfram, was supposed to be withdrawn from
Macsyma, on his request.
It is "no longer supported" in commercial Macsyma.
It is probably of no interest to run this code, at least to serious
physicists, because there are better (order of magnitude) faster programs.
But if it is of interest to look at the code, I found a copy dating from
about 1987. See
http://www.cs.berkeley.edu/~fateman/temp/gamalg.tar
which is source code. There is documentation in Clarkson's manual.
RJF