Should have the vehicle scanned for any trouble codes first. This would let you know what to look at. I suspect the Throttle Positioning Sensor and or the wiring plugin to the TPS. Wires like to break at the connector under the insulation of the wire. Also it could be an vacuum leak which is common on the Vortec engine along the intake manifold gasket. May want to re-torque the intake manifold bolts to like 15 ft. lbs.
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