not enough information. start from the beginning. What is your truck doing? Is it dying? Does the spark turn off? When you say it loses volts, do you mean all the volts as in loses power? Or that the volts are reduced?
Power for the coil comes from fuse #22 in the engine fuse box, left side of the engine compartment. Does the fuse lose power too when the coil is acting up? Fuse #22 powers the PCM power relay, the ignition module, the coil and the radio capacitor.