This is just me thinking and I have no evidence at all to back it up but theres something about this whole fuel pump thing that just dont ring true. What you said about the impeller swelling is what ive read as Toyotas answer from the get go, which to me would be a simple fix, put the older impellers back in the pumps or the older coatings on the impellers, either way something changed to cause this problem. Like you said, alcohol in the gas. I know several years ago Shell had an issue with too much sulfur in their gas and had to replace a bunch of fuel pumps, is that the issue now, I don't know, Shell is a popular fuel more so in some areas than others, and what I read the fuel pump issues are more problematic in some areas. Are they the same areas, I don't know. I do know that my particular truck seems to have better performance on Shell gas but doesn't run as smooth, runs smoother on BP but not quite the performance. In my mind if it was totally an impeller issue it should have been fixed a long time ago. JMO which probably means next to nothing.