So now, based on the fine commentators, a couple bird expert friends of mine, and additional study in my field guides, I can now tell you why this is a Plumbeous Vireo and not a Cassin's Vireo.
1. This bird is mostly grayish whereas a Cassin's Vireo significantly more olive and yellow.
2. The bill on this Plumbeous is larger and more stout than a Cassin's.
3. The edges of the secondaries are gray. A Cassin's will have greenish edges.
So, though I am a little embarrassed by my public error, I welcome the privilege of learning from my identification mistakes. The reason being wrong never felt so good is that Plumbeous Vireo is a new life bird!!! A little correction on my eBird checklist and bam!...Life bird #373!