On your 4.3 eating cap and rotors, I would recommend having the Cam Position Retard checked by someone with a full function scan tool. It is listed in the PID list as CMP Retard and is shown in degrees. The V8s were adjustable, but the V6s have a locked out distributor clamp. I like the see the CMP Retard between -5 and +5. If it is farther out either direction, it is correctable. First, slot the distributor clamp or install a V8 clamp. Watch the reading on a scan tool, raise the RPM to 1500, and turn the distributor until the scan tool reads between -2 to +2, and tighten the clamp. Then do a Crank Shaft Position Relearn for good measure. I have found on all the Vortec V6s I have seen with chronic cap failures, the retard is way off. If it is way off, I believe the cap and rotor are worked hard because the terminals and rotor tip are not in optimum alignment when the coil fires. This may sound strange, but that "distributor" is really just a switch, the computer completely controls when the spark happens. In fact, you can turn that distributor as far either way as you want and it will run, the spark just has to jump farther to the terminals internally. Most I have seen that were eating caps were around 15 degrees.