2010 Sierra 5.3
Whenever I run e85 or E30, one of my O2 sensors goes lazy. It is usually my driver side. Sometimes it will switch sides on the same trip with a key cycle. They both have less than 40,000 miles on them. the way it switches back and forth makes me think something in the tune but am I overlooking something mechanical or electrical? connections to both sensors are clean, corrosion free, watertight and good.
Photos on the below links.
https://photos.app.goo.gl/pVyFyvRnLXU8mwdPA
https://photos.app.goo.gl/eqK8FPmLNjxrALmE6