Does ps(1) also truncate at the same points? The kernel might only store so many characters or the regular API for retrieving process information only return a fixed-width field.

While looking up CPAN docs for Proc::ProcessTable, I found P9Y::ProcessTable, which seems to be a pure-Perl attempt at a similar module. Reading its code suggests that Solaris puts the command line and the filename in fixed-width fields in a "psinfo" file. I suspect that ps(1) will have the same problem and that you have encountered kernel limitations on Solaris and HP-UX.

Further digging into the Proc::ProcessTable source shows that the HP-UX and Solaris ports more-or-less directly return information from the kernel. Unless there are other ways to get the command line and filename, I think that you are stuck.

Look around in /proc/<PID>. On Linux, for example, the overall process status file contains only a command name, but the entire argv array is in cmdline.

Good call on Solaris. ps(1) truncates exactly the same way.
So, how does "/usr/ucb/ps auxww" get the full command line if not from the kernel?

Not the same for HP-UX. though.
ps(1) returns far more than Proc::ProcessTable.
I'm wondering if there is a way to configure this so I get back at least what ps gives me.

In both cases, more information is available, but Proc::ProcessTable does not know how to retrieve it.

You will need to find where ps(1) gets its information and then submit patches for Proc::ProcessTable. A good first place to look is /proc/<PID>. There may be additional files in there with useful information; this is certainly the case on Linux. Unfortunately, I don't have Solaris or HP-UX close at hand, so I can really only speculate on what you will need.