Section 231 (Engine Controls - Trouble Shooting - No Codes - 4.3L): INTERMITTENTS: Preliminary
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Perform the Diagnostic System Check - Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.