You say it bogs down, also that it stumbles. Is it more like a bumping or intermittent miss of the engine at low RPM when under a load? Like when going up hill? If so, I think its still ignition related. I've fought with this twice in the past on these engines. The first time it was plug wires. And they happen to be new wires, but were not AC Delco and only made it about 500 miles before the intermittent miss started. The other time was the rotor. Had the exact same symptoms. Replaced it, and the problem cleared up. Since you have already done cap and rotor, then you mite look at your wires.
the inevitable is coming...