I'm also working through an ABS / VSC / TRAC issue. I'm still figuring this out as I go, so take what I say with a grain of salt.
How are you reading the codes? On some systems (ultragauge, for example), ABS errors don't show up.
First, do what this guy does to get the codes.
YouTube
Both your ABS and VSC/TRAC will likely show codes, you have to check both.
The go to page 410 in the FSM to read the ABS codes and (413 for VSC.)
The chart doesn't spell it out, but I assume that the last two numbers of the DTC No. are the code you're getting from the truck. So if you're getting 3,4 code from the flashing light, that matches C0215 / 34: "Left rear wheel speed sensor signal malfunction"