My headlights flicker, engine looses power on.

Disconnect the small plug on the side of the generator, then drive the vehicle to see if the problems clear up. If they do, replace the generator and the battery unless it's less than about two years old. Due to their design, these generators develop huge voltage spikes that can destroy the internal diodes and voltage regulator, and they can interfere with computer sensor signals. As the battery ages, it loses it's ability to dampen and absorb those spikes. An old battery that seems to work fine is the biggest cause of repeat generator failures on GM vehicles.