is there a way to make criminals more desperate to escape? run harder, push cars to limit. more dangerous, shootout?

You could make the game harder for yourself by enabling hardcore mode;

In the scripts folder edit the lcpdfr.ini file with a text editor and change hardcore = false to hardcore = true.

This doesn't so much make the criminals tougher but the game gives less assistance to you, you don't have blips on the radar telling you where they are escaping to for example.

Alternatively, there is a mod/script called criminal acts that makes peds commit random crimes but I can't find it currently.