Terrible Fire 534 problem with OS3.9 and CPU speed

[Turrican2k]

Hello, thanks for the inclusion

I bought a Terrible Fire 534 and already installed it. For now it seems to be working; when I start the Amiga with Kick 1. 3 Workbench (diskette) the card even seems to be throttled to normal Amiga 500 speed (?). Sysinfo and various games confirm it to me.
If I start Kick3.1 Workbench (diskette) then the full resources of the accelerator card seem to be used (then runs on 33MHZ)

If I boot my old OS2.1 system with an SD card, it also works fine.

If I boot with my Workbench 3.9 system, the boot process takes half an eternity. When the Amiga finally started up I have to find out that the CPU is also throttled, like when I start with Kick1.3 and floppy disk.
If I connect the Int2 to the card and the Amiga, it will at least boot faster again, but I would like to save myself soldering work (under OS2.1 it works even without this connection).
I have to say that I deactivated the kickstart emulature under OS3.9.

How do I get my OS3.9 system to run properly? Are there software solutions, e.g. Add or remove drivers, libs?

Why does this card switch the CPU sometimes to 7MHZ and sometimes to 33MHZ?