Here are a few cold cases that might be worth checking into. Most are very unlikely; based on the timeline you guys have pieced together, I'm guessing that he started killing in Oregon in the '90s and didn't head to other states until about 2000, which rules out a lot of these, but if it was iffy I included it.
Kentucky
Jessica Wallace, remains found in March 2003 -
http://www.kentuckystatepolice.org/cold_case/post15coldcase9.html
They don't give very much information, but since Falls was in and out of the area when she vanished I included her.
Michelle Collins, last seen July 2004 -
http://www.kentuckystatepolice.org/cold_case/post11coldcase3.html
This one is possible but unlikely, especially since she's never been found.
Greta Henson, murdered in January 1992 -
http://www.kentuckystatepolice.org/cold_case/post10coldcase2.html
This one's unlikely because of the timeframe, but she was strangled and shot in her home.
Indiana
Amanda Lee Vanscyoc, murdered November 2001 -
http://www.in.gov/isp/2938.htm
Found nude and strangled near the Ohio River near Evansville.
Oregon
Angela Kreuger, murdered May 1996 -
http://www.portlandoregon.gov/police/article/458061
They're a little tight-lipped on the cause of death ("trauma"), but she was an escort.
Cassie Stevens, murdered July 1998 -
http://www.portlandoregon.gov/police/article/358069
Shot and killed; a drug user from Seattle who "needed to support her habit."
Linda Woods, murdered April 1992 -
http://www.portlandoregon.gov/police/article/485869
Another unlikely one, but she was strangled.
Veronica James, found murdered in January 1999 -
http://www.portlandoregon.gov/police/article/486175
Drug user and occasional sex worker. They don't say it but she was found in a canvas bag so she may have been dismembered. Died due to blunt force trauma.
Sarah Yarborough, murdered December 1992 -
http://www.kval.com/news/local/137105653.html
Check out the sketch on this one. Give Falls some terrible 90s hair and he could definitely be an aged version of the sketch. They have DNA, so if it was him they'll connect it.
Sharon Hiller, murdered November 1992 -
http://www.kval.com/news/local/Who-killed-Susan-Marie-Hiller-139304508.html
Exotic dancer found strangled in a river.
Also, I really think Oregon police should take a look at these cases:
http://www.kval.com/news/local/41372312.html
If he began killing in the early to mid-90s, these might have been some of his first victims, and he may not have escalated to dismembering bodies yet. The only ones that seem out of the realm of possibility are the the two 1980s cases. But one of them seems unconnected to the others; it's farther north, and it sounds like police had ideas but no evidence on the suspects there. The other could be coincidence, or could have been his inspiration.
And on an unrelated side note, there were a truly disturbing number of young African-American women being strangled, stabbed or both in Portland in the 1980s and early 1990s.