ULMB 180 Hz is not possible. For monitors that support 144Hz ULMB, there's only enough mathematical dotclock room to go up to 155 Hz without making the horizontal scan rate out-of-spec (number of scan lines per second). Maintaining exactly the same
horizontal scanrate number is extremely critical to tricking the firmware in letting you strobe at a non-NVIDIA-allowed refresh rate.
I have found that these ULMB tricks only works on certain monitors, so this is a very "hit-or-miss" trick. It definitely does not work on my ASUS ROG P278Q.
The fact that you even attempted 180Hz at all, indicates you didn't maintain the mathematic formula
and you should doublecheck what you're doing for 155Hz and less. Correctly mathematically-calculated exact Porch & Sync & Total numbers are exceedingly critical here for this trick. Can you rerun the math formula and screenshot your odd ULMB refreshrates, and we can tell you what you did wrong, or we can tell you your PG258Q doesn't support these ULMB hacks.
This is why Blur Busters doesn't (yet) have a HOWTO for this.
This is unofficial, bleeding-edge, forum-only stuff.
You have been hereby warned about the potential time-consuming nature of this type of attempted tweaking
Our research indicates only about 25% to 50% of ULMB monitor models may work with this trick and we don't have an official list of which monitors supports these undocumented ULMB monitors.
Keep tweaking, but the easiest way for us to tell you if you've tweaked correctly is a screenshot of your exact Porch counts, Total count, Sync count, Horizontal Refresh Rate (Scan Rate) -- not just your refresh rate. Then we can correctly tell you if you attempted the hack correctly. (I can pre-emptively tell you that you didn't do the hack correctly if you attempted 180 Hz
...)
Also, sometimes lowering ULMB refresh rate produces smoother/clearer motion -- due to the need for the triple lock for beautifully completely stutterless ULMB (framerate == stroberate == refreshrate). This is something harder at higher Hz -- see this thread:
Properly Using ULMB Beautifully or Competitively
No ULMB monitor has been capable of strobing at 180Hz. The 180 number comes from XL2540/XL2546 tweaking as a good compromise. Anything above ~180Hz veers closer towards the "bad" scale in the
strobe crosstalk photos.
Currently, the easiest overclockable GSYNC monitors are the ones with official overclockability (e.g. all the "165Hz" monitors). Those currently have successfully worked with the odd-ULMB-Hz trick, as well as the simultaneous "ULMB+GSYNC" trick. But that pretty much excludes 240Hz monitors (At this time).