Here's some stuff to check. The catalytic converter is a possible cause (part of the 'restricted exhaust' item)
"2000 Chevrolet Blazer - 2WD - 4.3L
Hesitation, Sag, Stumble
DEFINITION: The vehicle has a momentary lack of response when depressing the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall if it's severe enough.
Fuel System Checks
- Check the fuel pressure.
- Check the throttle position (TP) sensor for binding or sticking. Voltage should increase at a steady rate as the throttle moves toward wide open throttle (WOT).
- Check the manifold absolute pressure (MAP) sensor response and accuracy.
- Check for water contamination in the fuel.
- Check the canister purge system for proper operation.
- Perform the fuel injector coil test.
- Perform the fuel injector balance test.
- Check for low fuel pressure after a cold start or during a moderate or full throttle acceleration.
Ignition System Checks
- Check for damaged spark plug wires.
- Check for fouled spark plugs.
- Check for proper ignition system performance.
- Check the Service Bulletins for calibration updates.
- Check the generator output voltage.
- Check the EGR valve operation.
- Check for a restricted exhaust. "