After finally finding a way to check the status of the pushd stack, I found a bug in my patch whereby an extra directory is left on the pushd stack at the end of each run. As such, the version 5 patch changes from using 'goto end' to using 'exit /B !ERRORLEVEL!', along with some other changes related to that change. Also, because of that change, error handling is made a little easier, so I've changed around some of the messages and the conditions for printing them. Everything still seems to work.
For anyone testing this patch, I would suggest using the command "prompt $+%PROMPT%" if "$+" is not already part of your prompt. This will add a '+' character to the beginning of your prompt for every dir on the pushd stack.