Hmm . . . Power limit set works fine on my 6750XT.
Check for junction temperatures. If they are approaching 110 degrees, it is likely that your card downclocks and power throttles itself. Look into VBIOS, cable layout (should be separate cables for each 8pin) or some vague application conflict?
Try downgrading driver to 22.10.3 for example. Will power limit management return to normal?
Oh, then it must really be broken driver for you for some reason. . . Strange that it only affects this specific GPU. Try reporting as bug in driver and in email tech support for additional attention, i guess?