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Hello everyone,
I have a question I hope you can help me with. I have a 1995 GMC sierra 1500 reg cab tbi 5.7L engine and 4l60e transmission with 325K but only 15k on the motor and trans. When driving around town the engine stumbles when you give it part throttle, to say get up and approach or reverse. and when I take my foot off the gas the engines rpm will drop and sound like its not getting enough fuel. I've changed the IAC, Map sensor, temp sensor, temp sender, O2 sensor, checked fuel pressure(12.85 psi), checked fuel filter, timing(base timing set to zero with timing wire unplugged under dash). I've also check the egr valve and solenoid the fuel injectors and replaced the fuel pressure regulator.

Any idea what else would cause this to happen?

Also watched the timing advance with a timing light and set timing wire connected while manual raising the rpm at the throttle body looks like is only getting around 20 deg of advance between 2-4000 rpm and never higher. when idling at 700rpm(normal idle) the timing only register maybe 12 deg of advance.

Is that enough timing advance?

Any help will be greatly appreciated.
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