You can also try the century-old "classical" method. Find an old vacuum-tube oscilloscope with still working CRT (cathode-ray tube).
With some care you can get directly to the vertical deflection plates of the CRT, and connect your 5 kV peak lines to them. All other components originally connected to those vertical plates should be disconnected.
Then if the time base of the oscilloscope can run to ~ few MHz of your signal, then you should see the real shape of your signal on the screen.
Working with high voltages in the scope as well as on your RF line is dangerous and requires a good knowledge of what you are doing. But this is valid for using the HV probes, too. Take care!