Follow up for those who might have the issue.
Since I fixed the loose connection at the battery post, the ABS light has not come back on, when doing the same driving for that length of time since then would have set it off several times. Of course that is no proof it won't come on next time out in the truck.
Anyway thanks again to this trusty forum for helping out. This turns out to be a common problem with this generation of trucks and with all sorts of weird electrical causes and cures. So maybe my battery connection fix was the problem with mine (or not!)