.....Also, derailleur alignment can play a role in ghost shifting and a froggy chain.....

We have a winner. I thought I had the problem solved with the new cassette but yesterday I was climbing a hill and when I jumped out of the saddle to crest the hill in the 34 x 26 and the chain skipped again. So now I'm thinking it could be a bent derailleur hanger. Checked it out and sure enough it was bent. Knucklehead that I am while attempting to straighten it out with the Park Derailleur hanger alignment gauge I managed to overdo it and break the hanger. Fortunately the LBS had it in stock so I replaced it went for a ride and really worked the upper end of the cassette in the small chainring and finally it's shifting as it should.
I'm glad I saved the old cassette since it most likely still has about 3k miles in it.