No vehicle speed/ vibration issue

I have a 04 3.7 L 4x4 42RLE 3.73 axle KJ. I need a little help with an issue. The rear diff was whining at 99,000 miles. I had a used one put in. With the used one, on slow accelerations from a stop while turning, there is an occasional vibration going on. It last about 1-2 seconds. I'm not sure it is the used differential. I took it in to have the shop test drive it and it occurred once for them. The put some diff additive in it to take a shot at resolving it. I then picked it up and the ABS light and Brake Warning light came on with no vehicle speed reporting while driving. It's back in the shop. I'm trying to figure out if the vehicle speed/brake light/ABS light issue is related to the installed used diff or because of something else. Does anyone know where the vehicle speed sensor is? Is it an ABS controller CAN message? Is it a hard wired sensor? Is the vehicle speed sensor on the rear diff or the trans? If the vehicle speed comes from the ABS, where is the ABS controller (is it part of the rear end assembly)? Also, does anyone have any ideas what the vibration could be?