It started out decending at 2300ft/min, then it went to 3050ft/min all the way down to 4225ft/min and then back up the scale to the point of impact. Is this normal if the aircraft was on autopilot?
Yes if the descent mode (OP DES) was pitching the nose up/down to maintain a selected MN/IAS. As the head/tail winds change during the descent the pitch attitude (and vertical speed) will change to maintain the selected speed.