15.0 mpg to 21.6 mpg!

No, not saying that. For a while I thought I had a 3.55's based on using online gear calculators, and my rpm at speed, tire size, etc. But finally at some point (when replacing the fuel sending unit), I spun the tire and counted the driveshaft revs, and it was CLEAR it was a 3.23.

It was at that time I was like, "no way I'm trying to find a 3.55, it turns too many rpm as it is." It was then I decided to stay with the 3.23's, and just replace the open diff with the TrueTrac. For a minute (when I thought I had 3.55s) I was thinking I would try to find 3.23 gears. I'm glad, as it turned out, that it had 3.23s all along.

I just didn't follow this thread up well enough to add all those details.