Guitar Pro (from which .gp5 projects originate) allows users to export their projects to tablatures and music sheets as well as several audio files, including .wav files. So it is your best and probably only choice for GP5 to WAV conversion.
Convert Guitar Pro 5 project to WAVe PCM Sound, standard Windows sound format.
We have found 2 software records in our database eligible for .gp5 to .wav file format conversion.
Microsoft Windows software - convert gp5 to wav on Windows
Multi-track editor and music composer for guitars
Convert from gp5 file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned gp5 to wav. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert gp5 to wav on OS X
Mac version of the popular tablature editor