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1985 GMC 1500 - Carb?

I am having trouble with my truck hesitating when its under a heavy load. it has a quadrajet carb, I have recently changed the plugs wires cap rotor pcv coil coil cap. it seams to run fine until I need the four barrel to kick in, it will loose power hesitate ,sputter, and also has a signifigant spark knock. any ideas about what the malfunction is?

it has a 4.3 v-6 with a 4 barrel carb

Check for vacuum leaks.

I thought I found them all. i’ll check for more. thanks