What was the last time Washington voted more R than Oregon? What was the last time Oregon and/or Washington was more Republican than the nation at large?
Don't know the answer to the first question, but I'm pretty sure the answer to the second question would be 1976 when Gerald Ford won Washington and Oregon while losing nationally.
Why did he do so well in the Pacific Northwest?
I don't know any specific reasons in terms of the demographic breakdowns of Washington and Oregon, but centrist type Republicans used to get elected to the U.S Senate from both states at around this same time: Dan Evans in Washington (Senator from 1982-1988 and Governor prior to that succeeding Democrat Henry Scoop Jackson in the Senate), Bob Packwood and Mark Hatfield in Oregon (the centrist Democrat Henry 'Scoop' Jackson was the 4th Senator around this same time along along with Warren Magnuson) so, I don't think it's a surprise that a centrist type Republican like Gerald Ford would do well in both of those states. The centrist Richard Nixon in 1960, 1968 and 1972 also was generally popular in both states, so this wasn't just a personal vote for Ford.
In Washington Slade Gorton defeated Warren Magnuson in the Republican wave year in 1980 but he was quite a bit more conservative. He also was defeated in 1986, got reelected to the Senate in 1988 and finally put down for good in 2000. He doesn't really fit into this as he was more conservative, but I mention him just to be a completist.