The timing on a 1994 Chevy truck can be set by Adjusting the distributor. To do this, first locate the distributor cap and rotate it until you find the number one cylinder. Once you have found the number one cylinder, remove the distributor cap and look at the rotor. The rotor should be pointing to the number one spark plug wire on the distributor cap. If it is not, then loosen the hold down clamp and rotate the distributor until the rotor is pointing to that spark plug wire. Once you have done that, tighten down the hold down clamp and put the distributor cap back on.