"what exactly does the mileliminator do, in technical terms?"

Sends a voltage signal to the PCM that reads the Pre-cats are working fine.

Also read this.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=trouble&Number=1177534&page=&view=&sb=5&o=&fpart=1&vc=1

"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles