The reason for the surging (and turning off cruise control) is that the turn signal is grounding through the brake light. so when the turn signal illuminates, the vehicle thinks you hit the brake pedal as well. this causes the cruise control to disengage and the torque converter to release (causing the rpms to jump) while the rpms are surging, either taking your foot completely off the gas or putting it hard on the gas will reduce the surging until you get it completely taken care of.