That TWRP 2.5 is really hard to kill :)
Ok, here is how i did it without spflas tools.
1. First installed dev V6 5.4.10., rebooted, still TWRP!?
2. Then flashed stock via mobileuncle tools, rebooted back to the system to let the original install-recovery.sh script do it's patching
3. Rebooted...