P0300 Multiple misfire

Hi everyone. I have 1996 3.5 engine. It has 70,000 miles. Recently I changed Intake Mainifold Gasket due to rough idle. While changing gasket replaced plugs and wires. Engine ran great for 10 - 20 miles then rough idle with engine light blinking. Code is 43 ( P0300 multiple misfire obd II). I changed plugs and wires again and no changes. What can cause this P0300. I'm going nuts here!!!
Thanks

Hi everyone. I have 1996 3.5 engine. It has 70,000 miles. Recently I changed Intake Mainifold Gasket due to rough idle. While changing gasket replaced plugs and wires. Engine ran great for 10 - 20 miles then rough idle with engine light blinking. Code is 43 ( P0300 multiple misfire obd II). I changed plugs and wires again and no changes. What can cause this P0300. I'm going nuts here!!!
Thanks
Did you ever find your problem? I have a 97 lhs and I have a misfire #6. I changed everything (coil pack, Spark plugs, wires, injector, and intake gasket). Please Let me know

Thanks

Did you ever find your problem? I have a 97 lhs and IThanks
You must check for a vacum leak at the intake manifold gasket. Just add
propane below the intake manifold you can access it at the very front between the engine block and the intake while idling turn propane on a little and see if the idle quality changes if it changes you know you must
change the intake gasket