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GMC Truck
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1988
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R 2500 P/U 2WD V8-454 7.4L
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Repair and Diagnosis
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Transmission and Drivetrain
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Automatic Transmission/Transaxle
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Testing and Inspection
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Symptom Related Diagnostic Procedures
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No Part Throttle Downshifts
No Part Throttle Downshifts
1. Vacuum modulator assembly.
2. Modulator valve.
3. Regulator valve train.
4. Control valve assembly has stuck 3-2 valve or broken spring.