I'm having a tough time with my ABS system in my F-150. (199 F150, 4X4, rear drum w/4 wheel ABS)

I had the truck in a while back for some diagnosis (low speed ABS activation issue) and the shop determined that the Left front ABS sensor had thrown a code. When I bought the truck a year back, the ABS light came on a couple times, but has been off all summer long. The low speed ABS activation issue has ALWAYS been present. Fast forward to Friday evening. I finally got around to replacing the drivers front wheel bearing assembly, and did both front rotors/pads and the Drivers side upper control arm and lower balljoint while I was at it. Drove the truck home, still no ABS light. I came to a stop a couple of times and THOUGHT I felt that low speed ABS activation happen, but it could have been just teh truck creaking. Tonight, I definitely felt the ABS activate like it used to, however, it was much lighter than it had been in the past. This happens at 3 or so MPH and less.

So the breakdown:

I have low speed ABS activation.
Prior to the wheel bearing/sensor replacement on the drivers side, it happened almost every single time i stopped. NOW it happens maybe every 5th time I stop.

NO ABS light has came on at all, other than about a year ago intermittently. NO ABS light since I changed the bearing/sensor

The truck still needs to be aligned, as it IS cambered out a bit, and my tires are almost bald, if that matters at all.

Any ideas? Do you have to clear the ABS codes after replacing a sensor for it to work properly?