If teh SamKnows box is reporting 37/8 on a wired connection to the router and you are seeing the speeds you report which are way lower then it starts to point to a wireless interface issue. It could be severe interference, or a failing transmitter stage in the Asus.
Without actual connection stats and inability to get a wired connection there is little else to suggest as to the cause. You could try powering everything down, waiting for an hour and then bringing it all back up - but before that see if there is any way to get a wired connection to teh router.
M H C
taurus excreta cerebrum vincit