Maybe normal
My truck and have read of other complaints (I would say its a common phenomenon). The anti lock brake cause a hydro assist dump too. Say braking at a stop sign with a rough patch of road. The rear wants to skid but the antilock brake dumps pressure. If you hit a bump (curb) while turning in your driveway while braking thats probably what triggered it. I get the dump of assist usually going slow last 10-20 ft before a stop sign where pavement is wrinkled and usually has a bit of gravel that makes the rearend loose traction. I loose firmness in brake pedal and have to stand on brakes to keep from over shooting the stop sign - its not a good feeling. It only happens when I am braking kind of hard. The steering wheel also feels different but I have never been turning real hard at the time.
Maybe new shocks would help but I don't know. Test it a little and see if you can make it come and go. Brake a little hard and turn while loose traction and some bumps and see if it repeats the feeling you experienced before trying to throw money at it. Unfortunately it may be normal.
97 5spd K2500 Ext Cab short Bed ~160K miles.
TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.