Loss of power

Loss of Power
1993 GMC Sonoma – 4.3L (“Z” Code) – 186,000 miles

Scenario: Intermittent Loss of Power primarily when climbing hills but occasionally with hard acceleration.

Symptoms: Loses power without backfire, odors, smoke, vibration, or mechanical sounds. Check engine light comes on – sometimes. If accelerator is depressed further to compensate, it loses power faster. There is an apparent “sweet spot” in the accelerator where power is not further reduced – per se – during which vehicle continues at current speed on the level and slows when climbing hills. No acceleration is possible, or marginal at best, during these episodes. Engine may also start and then stall which it had not done previously.

I would estimate that the engine runs fine 95% of the time.

Recent Work: Plugs (Bosch Platinum – first time used), wires, distributor cap & rotor, ignition module, fuel filter, and catalytic convertor replaced. All of these parts except the ignition module were installed just prior to this problem. Ignition module was replaced after the engine shut down (with two quick, but muted, backfires) on the highway with less than 20 miles driven since the tune-up.

Mechanic said his scanner indicated “no communication” or something similar when he plugged into the diagnostic port.

Any ideas as to the cause/source of the problem and how to correct it?