You must have been filing you income tax from Oregon the last 3 of five years so you know you pay capital gains. I myself have never heard of the 3% additional tax you are speaking of. I just left a message for the best tax CPA I know to find that answer as I surely want to know! I will post my findings when I get them.
Thanks for the great question!
I would highly reccomend that you talk to an accountant . We as Realtors are experts at listing and selling homes. Accountants/Attorneys will give you the best advice in these areas.