I have solved my SL/IP problem.  The solution was to use sliplogin
instead of slattach.  Thanks everybody.

     My next problem is that I want to dynamic SL/IP.  I'm told that
this requires spitting an IP address out right before entering SL/IP
mode.  I have a method of assigning IP addresses, but not spitting them
out.  The problem is that sliplogin detaches from the controlling tty
and routes stdout/stderr to /dev/null before calling slip.login, so my
echo statement in slip.login does nothing.  What is the proper procedure
for doing this?