The Caspers LED cap is designed to work correctly assuming that your cam drive is within OEM spec and you are using a Delco ignition module or approved equivalent.
The LED cap will not work properly if the internal thrust plate on your cam sensor drive is badly worn. If there is too much end-play, the interrupter window could fall out of the sense range. Always be sure your sensor drive is within factory spec, and send it out for rebuilding if you're not sure. As a rule, if the mileage on the car is above 50,000, it's probably worn and out of spec.
Also, if the module is an aftermarket style, it could present issues with both the cam and the crank sensor. Some aftermarket modules don't supply the GM-spec voltages to the sensors which affect the operation of the Hall-Effect properties, and can also affect the proper operation of the LED on the cap.