I also found this forum after trying to investigate odd chicken texture.
On at least three occasions in the past year using boneless chicken breast purchased at either WalMart, Giant or Bottom Dollar grocery stores we've experienced this 'odd chicken.'
The most recent was last night. We had 4 very large chicken breasts and they were cooked on the stove-top in a cream-of-chicken soup based gravy. This is normally served over rice and is a dish we are very accustomed to. It is very difficult to describe what was 'wrong' with the meat. It looked like chicken... and cooked up like chicken... it pretty much tasted like chicken but not like we're used to. The texture can only be described as 'fake' or maybe 'plastic-y.' While the meat appeared to have the normal string-like texture of chicken the experience of eating it was much more like pressed chicken or chicken-roll.
As mentioned... these were large breasts. If they were from an old chicken I'd fully expect them to be tougher, stringier, chewier... but the opposite was true. I could easily slice through the entire thing with the edge of a fork. Chewing it, it felt unnatural... like something was wrong with it. The flavor was alright... but a little blah... but then some chicken is tastier than others.
We ate some and ended up trashing the rest. Even my cat didn't want to eat the meat (creepy).
Thanks for listening and sharing.