Shaking??? an rough idol

I would suggest that you have the engine and transmission mounts checked.

check your plugs and wires they might be causing the rough idle, and check ur fuel filter, that might casue it, i need more info in the shake, is it up front or out back, what gear are you in, how many miles are on the clutch, did it just start shaking, or did it gradually get worse?

ill check them right now but its the shake is coming from the back. Im in overdrive when it happens. and im not sure how many miles are on the clutch. The shaking started right after the truck was lowerd 4In

check your vacum lines the stock idle speed for the 4.3 l is anywhere from 650 + or - 25 or so rpms, if your plugs and wires are in good shape then look at the front end such as ball joints or control arm bushings. Also inspect your engine for leaks around the head gasket seals if your truck has upwards of 140000 mi then it might be time for a reseal. These engines are solid and can last for a long time but they need mantience.

if this started after it was lowered your alignment may be off. also another very common problem with gm cars is the idle-air control valve check both of those and also make sure your tires are the same size and have equal tread wear

have you tryed a new cap and rotor this might help

Thanks for all your help we put all new spark plugs, spark plug wires, a new distributer cap and rotar, and new u joints. Everything RUNS perfect shes finally actually got some kick to her. thanks again

it might be ur center link and/or your idler arm.